diff --git a/include/plasp/pddl/Domain.h b/include/plasp/pddl/Domain.h
index d9261ca..42bcc56 100644
--- a/include/plasp/pddl/Domain.h
+++ b/include/plasp/pddl/Domain.h
@@ -26,7 +26,8 @@ class Domain
 		Domain(Context &context);
 
 	public:
-		void readPDDL();
+		void findSections();
+		void parse();
 
 		void setName(std::string name);
 		const std::string &name() const;
@@ -66,10 +67,20 @@ class Domain
 		Context &m_context;
 
 		std::string m_name;
+
+		utils::Parser::Position m_requirementsPosition;
 		Requirements m_requirements;
-		expressions::PrimitiveTypes m_primitiveTypes;
+
+		utils::Parser::Position m_typesPosition;
+		expressions::PrimitiveTypes m_types;
+
+		utils::Parser::Position m_constantsPosition;
 		expressions::Constants m_constants;
-		expressions::PredicateDeclarations m_predicateDeclarations;
+
+		utils::Parser::Position m_predicatesPosition;
+		expressions::PredicateDeclarations m_predicates;
+
+		std::vector<utils::Parser::Position> m_actionPositions;
 		std::vector<std::unique_ptr<Action>> m_actions;
 };
 
diff --git a/include/plasp/pddl/expressions/InitialState.h b/include/plasp/pddl/InitialState.h
similarity index 68%
rename from include/plasp/pddl/expressions/InitialState.h
rename to include/plasp/pddl/InitialState.h
index ff94409..fbbd5f8 100644
--- a/include/plasp/pddl/expressions/InitialState.h
+++ b/include/plasp/pddl/InitialState.h
@@ -7,20 +7,27 @@ namespace plasp
 {
 namespace pddl
 {
-namespace expressions
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// InitialState
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class InitialState
 {
+	public:
+		static std::unique_ptr<InitialState> parseDeclaration(Context &context, const Problem &problem);
 
-////////////////////////////////////////////////////////////////////////////////////////////////////
-//
-// Type
-//
-////////////////////////////////////////////////////////////////////////////////////////////////////
+	public:
+		const Expressions &facts() const;
 
-ExpressionPointer parseInitialState(Context &context);
+	private:
+		Expressions m_facts;
+};
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-}
 }
 }
 
diff --git a/include/plasp/pddl/Problem.h b/include/plasp/pddl/Problem.h
index c360b5b..37bae97 100644
--- a/include/plasp/pddl/Problem.h
+++ b/include/plasp/pddl/Problem.h
@@ -3,6 +3,7 @@
 
 #include <plasp/pddl/Context.h>
 #include <plasp/pddl/Expression.h>
+#include <plasp/pddl/InitialState.h>
 #include <plasp/pddl/Requirement.h>
 
 namespace plasp
@@ -21,7 +22,7 @@ class Problem
 	public:
 		Problem(Context &context, Domain &domain);
 
-		void readPDDL();
+		void parse();
 
 		bool isDeclared() const;
 
@@ -37,6 +38,9 @@ class Problem
 		expressions::Constants &objects();
 		const expressions::Constants &objects() const;
 
+		InitialState &initialState();
+		const InitialState &initialState() const;
+
 		void checkConsistency();
 
 	private:
@@ -49,6 +53,8 @@ class Problem
 
 		void parseObjectSection();
 
+		void parseInitialStateSection();
+
 		Context &m_context;
 		Domain &m_domain;
 		bool m_isDeclared;
@@ -57,6 +63,8 @@ class Problem
 		Requirements m_requirements;
 
 		expressions::Constants m_objects;
+
+		std::unique_ptr<InitialState> m_initialState;
 };
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/include/plasp/pddl/expressions/Constant.h b/include/plasp/pddl/expressions/Constant.h
index 4051a03..bd642cc 100644
--- a/include/plasp/pddl/expressions/Constant.h
+++ b/include/plasp/pddl/expressions/Constant.h
@@ -27,7 +27,8 @@ class Constant: public Expression
 		static void parseTypedDeclaration(Context &context, Problem &problem);
 		static void parseTypedDeclarations(Context &context, Problem &problem);
 
-		static Constant *parseAndFind(Context &context, const ExpressionContext &expressionContext);
+		static Constant *parseAndFind(Context &context, const Domain &domain);
+		static Constant *parseAndFind(Context &context, const Problem &problem);
 
 	public:
 		void accept(ExpressionVisitor &expressionVisitor) const override;
diff --git a/include/plasp/pddl/expressions/Predicate.h b/include/plasp/pddl/expressions/Predicate.h
index c71e1d7..14dc971 100644
--- a/include/plasp/pddl/expressions/Predicate.h
+++ b/include/plasp/pddl/expressions/Predicate.h
@@ -21,6 +21,7 @@ class Predicate: public Expression
 	public:
 		static PredicatePointer parse(std::string name, Context &context,
 			ExpressionContext &expressionContext);
+		static PredicatePointer parse(std::string name, Context &context, const Problem &problem);
 
 	public:
 		void accept(ExpressionVisitor &expressionVisitor) const override;
diff --git a/src/plasp/pddl/Description.cpp b/src/plasp/pddl/Description.cpp
index fd3f5fe..8566402 100644
--- a/src/plasp/pddl/Description.cpp
+++ b/src/plasp/pddl/Description.cpp
@@ -106,12 +106,12 @@ void Description::parseContent()
 		throw ConsistencyException("No PDDL domain specified");
 
 	m_context.parser.seek(m_domainPosition);
-	m_domain->readPDDL();
+	m_domain->parse();
 
 	if (m_problemPosition != -1)
 	{
 		m_context.parser.seek(m_problemPosition);
-		m_problem->readPDDL();
+		m_problem->parse();
 	}
 }
 
@@ -119,41 +119,45 @@ void Description::parseContent()
 
 void Description::findSections()
 {
-	while (true)
+	auto &parser = m_context.parser;
+
+	parser.skipWhiteSpace();
+
+	while (!parser.atEndOfStream())
 	{
-		m_context.parser.skipWhiteSpace();
+		const auto position = parser.position();
 
-		if (m_context.parser.atEndOfStream())
-			return;
+		parser.expect<std::string>("(");
+		parser.expect<std::string>("define");
+		parser.expect<std::string>("(");
 
-		const auto position = m_context.parser.position();
-
-		m_context.parser.expect<std::string>("(");
-		m_context.parser.expect<std::string>("define");
-		m_context.parser.expect<std::string>("(");
-
-		if (m_context.parser.probe<std::string>("domain"))
+		if (parser.probe<std::string>("domain"))
 		{
 			if (m_domainPosition != -1)
-				throw utils::ParserException(m_context.parser, "PDDL description may not contain two domains");
+				throw utils::ParserException(parser, "PDDL description may not contain two domains");
 
 			m_domainPosition = position;
+
+			parser.seek(position);
+			m_domain->findSections();
 		}
 		else if (m_context.parser.probe<std::string>("problem"))
 		{
 			if (m_problemPosition != -1)
-				throw utils::ParserException(m_context.parser, "PDDL description may currently not contain two problems");
+				throw utils::ParserException(parser, "PDDL description may currently not contain two problems");
 
 			m_problemPosition = position;
+
+			skipSection(parser);
+			skipSection(parser);
 		}
 		else
 		{
-			const auto sectionIdentifier = m_context.parser.parse<std::string>();
-			throw utils::ParserException(m_context.parser, "Unknown PDDL section \"" + sectionIdentifier + "\"");
+			const auto sectionIdentifier = parser.parse<std::string>();
+			throw utils::ParserException(parser, "Unknown PDDL section \"" + sectionIdentifier + "\"");
 		}
 
-		skipSection(m_context.parser);
-		skipSection(m_context.parser);
+		m_context.parser.skipWhiteSpace();
 	}
 }
 
diff --git a/src/plasp/pddl/Domain.cpp b/src/plasp/pddl/Domain.cpp
index 9e0a50b..c0332ea 100644
--- a/src/plasp/pddl/Domain.cpp
+++ b/src/plasp/pddl/Domain.cpp
@@ -11,6 +11,7 @@
 #include <plasp/pddl/expressions/Variable.h>
 #include <plasp/utils/IO.h>
 #include <plasp/utils/ParserException.h>
+#include <plasp/utils/ParserWarning.h>
 
 namespace plasp
 {
@@ -24,35 +25,129 @@ namespace pddl
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 Domain::Domain(Context &context)
-:	m_context(context)
+:	m_context(context),
+	m_requirementsPosition{-1},
+	m_typesPosition{-1},
+	m_constantsPosition{-1},
+	m_predicatesPosition{-1}
 {
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void Domain::readPDDL()
+void Domain::findSections()
 {
-	m_context.parser.expect<std::string>("(");
-	m_context.parser.expect<std::string>("define");
-	m_context.parser.expect<std::string>("(");
-	m_context.parser.expect<std::string>("domain");
+	auto &parser = m_context.parser;
+
+	parser.expect<std::string>("(");
+	parser.expect<std::string>("define");
+	parser.expect<std::string>("(");
+	parser.expect<std::string>("domain");
 
 	m_name = m_context.parser.parseIdentifier(isIdentifier);
 
+	std::cout << "Found domain " << m_name << std::endl;
+
+	parser.expect<std::string>(")");
+
+	const auto setSectionPosition =
+		[&](const std::string &sectionName, auto &sectionPosition, const auto value, bool unique = false)
+		{
+			if (unique && sectionPosition != -1)
+				throw utils::ParserException(parser, "Only one \":" + sectionName + "\" section allowed");
+
+			sectionPosition = value;
+		};
+
+	parser.skipWhiteSpace();
+
+	// Find sections
+	while (parser.currentCharacter() != ')')
+	{
+		const auto position = parser.position();
+
+		parser.expect<std::string>("(");
+		parser.expect<std::string>(":");
+
+		// Save the parser position of the individual sections for later parsing
+		if (parser.probe<std::string>("requirements"))
+			setSectionPosition("requirements", m_requirementsPosition, position, true);
+		else if (parser.probe<std::string>("types"))
+			setSectionPosition("types", m_typesPosition, position, true);
+		else if (parser.probe<std::string>("constants"))
+			setSectionPosition("constants", m_constantsPosition, position, true);
+		else if (parser.probe<std::string>("predicates"))
+			setSectionPosition("predicates", m_predicatesPosition, position, true);
+		else if (parser.probe<std::string>("action"))
+		{
+			m_actionPositions.emplace_back(-1);
+			setSectionPosition("action", m_actionPositions.back(), position);
+		}
+		else if (parser.probe<std::string>("functions")
+			|| parser.probe<std::string>("constraints")
+			|| parser.probe<std::string>("durative-action")
+			|| parser.probe<std::string>("derived"))
+		{
+			parser.seek(position);
+			m_context.logger.parserWarning(parser, "Section type currently unsupported");
+			parser.advance();
+		}
+		else
+		{
+			const auto sectionIdentifier = parser.parseIdentifier(isIdentifier);
+
+			parser.seek(position);
+			throw utils::ParserException(m_context.parser, "Unknown domain section \"" + sectionIdentifier + "\"");
+		}
+
+		// Skip section for now and parse it later
+		skipSection(parser);
+
+		parser.skipWhiteSpace();
+	}
+
+	parser.expect<std::string>(")");
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+void Domain::parse()
+{
+	auto &parser = m_context.parser;
+
 	std::cout << "Parsing domain " << m_name << std::endl;
 
-	m_context.parser.expect<std::string>(")");
-
-	while (true)
+	if (m_requirementsPosition != -1)
 	{
-		m_context.parser.skipWhiteSpace();
-
-		if (m_context.parser.probe(')'))
-			break;
-
-		parseSection();
+		parser.seek(m_requirementsPosition);
+		parseRequirementSection();
 	}
 
+	if (m_typesPosition != -1)
+	{
+		parser.seek(m_typesPosition);
+		parseTypeSection();
+	}
+
+	if (m_constantsPosition != -1)
+	{
+		parser.seek(m_constantsPosition);
+		parseConstantSection();
+	}
+
+	if (m_predicatesPosition != -1)
+	{
+		parser.seek(m_predicatesPosition);
+		parsePredicateSection();
+	}
+
+	for (size_t i = 0; i < m_actionPositions.size(); i++)
+		if (m_actionPositions[i] != -1)
+		{
+			parser.seek(m_actionPositions[i]);
+			parseActionSection();
+		}
+
 	computeDerivedRequirements();
 }
 
@@ -81,14 +176,14 @@ const Requirements &Domain::requirements() const
 
 expressions::PrimitiveTypes &Domain::types()
 {
-	return m_primitiveTypes;
+	return m_types;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 const expressions::PrimitiveTypes &Domain::types() const
 {
-	return m_primitiveTypes;
+	return m_types;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -109,14 +204,14 @@ const expressions::Constants &Domain::constants() const
 
 expressions::PredicateDeclarations &Domain::predicates()
 {
-	return m_predicateDeclarations;
+	return m_predicates;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 const expressions::PredicateDeclarations &Domain::predicates() const
 {
-	return m_predicateDeclarations;
+	return m_predicates;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -135,52 +230,21 @@ const std::vector<std::unique_ptr<Action>> &Domain::actions() const
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void Domain::parseSection()
+void Domain::parseRequirementSection()
 {
 	auto &parser = m_context.parser;
 
 	parser.expect<std::string>("(");
 	parser.expect<std::string>(":");
+	parser.expect<std::string>("requirements");
 
-	// TODO: check order of the sections
-	if (parser.probe<std::string>("requirements"))
-		parseRequirementSection();
-	else if (parser.probe<std::string>("types"))
-		parseTypeSection();
-	else if (parser.probe<std::string>("constants"))
-		parseConstantSection();
-	else if (parser.probe<std::string>("predicates"))
-		parsePredicateSection();
-	else if (parser.probe<std::string>("action"))
-		parseActionSection();
-	else if (parser.probe<std::string>("functions")
-		|| parser.probe<std::string>("constraints")
-		|| parser.probe<std::string>("durative-action")
-		|| parser.probe<std::string>("derived"))
+	while (parser.currentCharacter() != ')')
 	{
-		std::cout << "Skipping section" << std::endl;
-		skipSection(m_context.parser);
-	}
-	else
-	{
-		const auto sectionIdentifier = parser.parseIdentifier(isIdentifier);
-		throw utils::ParserException(m_context.parser, "Unknown domain section \"" + sectionIdentifier + "\"");
-	}
-}
-
-////////////////////////////////////////////////////////////////////////////////////////////////////
-
-void Domain::parseRequirementSection()
-{
-	m_context.parser.skipWhiteSpace();
-
-	while (m_context.parser.currentCharacter() != ')')
-	{
-		m_context.parser.expect<std::string>(":");
+		parser.expect<std::string>(":");
 
 		m_requirements.emplace_back(Requirement::parse(m_context));
 
-		m_context.parser.skipWhiteSpace();
+		parser.skipWhiteSpace();
 	}
 
 	// TODO: do this check only once the problem is parsed
@@ -188,7 +252,7 @@ void Domain::parseRequirementSection()
 	if (m_requirements.empty())
 		m_requirements.emplace_back(Requirement::Type::STRIPS);
 
-	m_context.parser.expect<std::string>(")");
+	parser.expect<std::string>(")");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -258,60 +322,82 @@ void Domain::computeDerivedRequirements()
 
 void Domain::parseTypeSection()
 {
+	auto &parser = m_context.parser;
+
+	parser.expect<std::string>("(");
+	parser.expect<std::string>(":");
+	parser.expect<std::string>("types");
+
 	checkRequirement(Requirement::Type::Typing);
 
-	m_context.parser.skipWhiteSpace();
+	parser.skipWhiteSpace();
 
 	// Store types and their parent types
-	while (!m_context.parser.probe(')'))
+	while (parser.currentCharacter() != ')')
 	{
-		if (m_context.parser.currentCharacter() == '(')
-			throw utils::ParserException(m_context.parser, "Only primitive types are allowed in type section");
+		if (parser.currentCharacter() == '(')
+			throw utils::ParserException(parser, "Only primitive types are allowed in type section");
 
 		expressions::PrimitiveType::parseTypedDeclaration(m_context, *this);
 
-		m_context.parser.skipWhiteSpace();
+		parser.skipWhiteSpace();
 	}
+
+	parser.expect<std::string>(")");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 void Domain::parseConstantSection()
 {
-	m_context.parser.skipWhiteSpace();
+	auto &parser = m_context.parser;
+
+	parser.expect<std::string>("(");
+	parser.expect<std::string>(":");
+	parser.expect<std::string>("constants");
 
 	// Store constants
 	expressions::Constant::parseTypedDeclarations(m_context, *this);
 
-	m_context.parser.expect<std::string>(")");
+	parser.expect<std::string>(")");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 void Domain::parsePredicateSection()
 {
-	m_context.parser.skipWhiteSpace();
+	auto &parser = m_context.parser;
+
+	parser.expect<std::string>("(");
+	parser.expect<std::string>(":");
+	parser.expect<std::string>("predicates");
+
+	parser.skipWhiteSpace();
 
 	// Store predicates and their arguments
-	while (m_context.parser.currentCharacter() != ')')
+	while (parser.currentCharacter() != ')')
 	{
 		expressions::PredicateDeclaration::parse(m_context, *this);
 
-		m_context.parser.skipWhiteSpace();
+		parser.skipWhiteSpace();
 	}
 
-	m_context.parser.expect<std::string>(")");
+	parser.expect<std::string>(")");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 void Domain::parseActionSection()
 {
-	m_context.parser.skipWhiteSpace();
+	auto &parser = m_context.parser;
+
+	parser.expect<std::string>("(");
+	parser.expect<std::string>(":");
+	parser.expect<std::string>("action");
 
 	Action::parseDeclaration(m_context, *this);
 
-	m_context.parser.expect<std::string>(")");
+	parser.expect<std::string>(")");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/src/plasp/pddl/Expression.cpp b/src/plasp/pddl/Expression.cpp
index e5e88da..4014abe 100644
--- a/src/plasp/pddl/Expression.cpp
+++ b/src/plasp/pddl/Expression.cpp
@@ -4,6 +4,7 @@
 #include <plasp/pddl/Domain.h>
 #include <plasp/pddl/ExpressionContext.h>
 #include <plasp/pddl/Identifier.h>
+#include <plasp/pddl/IO.h>
 #include <plasp/pddl/expressions/And.h>
 #include <plasp/pddl/expressions/Imply.h>
 #include <plasp/pddl/expressions/Not.h>
@@ -33,10 +34,10 @@ ExpressionPointer parsePredicate(Context &context, ExpressionContext &expression
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-[[noreturn]] void throwUnsupported(const utils::Parser &parser,
-	const std::string &expressionIdentifier)
+inline void warnUnsupported(Context &context, const std::string &expressionIdentifier)
 {
-	throw utils::ParserException(parser, "Expression type \"" + expressionIdentifier + "\" currently unsupported in this context");
+	context.logger.parserWarning(context.parser, "Expression type \"" + expressionIdentifier + "\" currently unsupported in this context");
+	skipSection(context.parser);
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -58,7 +59,9 @@ ExpressionPointer parsePreconditionExpression(Context &context,
 	else if (expressionIdentifier == "forall"
 		|| expressionIdentifier == "preference")
 	{
-		throwUnsupported(context.parser, expressionIdentifier);
+		warnUnsupported(context, expressionIdentifier);
+
+		return nullptr;
 	}
 	else
 		expression = parseExpressionContent(expressionIdentifier, context, expressionContext);
@@ -116,7 +119,9 @@ ExpressionPointer parseExpressionContent(const std::string &expressionIdentifier
 		|| expressionIdentifier == ">="
 		|| expressionIdentifier == "<=")
 	{
-		throwUnsupported(context.parser, expressionIdentifier);
+		warnUnsupported(context, expressionIdentifier);
+
+		return nullptr;
 	}
 
 	auto &predicateDeclarations = expressionContext.domain.predicates();
@@ -132,7 +137,7 @@ ExpressionPointer parseExpressionContent(const std::string &expressionIdentifier
 	if (match != predicateDeclarations.cend())
 		return expressions::Predicate::parse(expressionIdentifier, context, expressionContext);
 
-	throw utils::ParserException(context.parser, "Expression \"" + expressionIdentifier + "\" not allowed in this context");
+	throw utils::ParserException(context.parser, "Unknown expression \"" + expressionIdentifier + "\"");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -150,7 +155,9 @@ ExpressionPointer parseEffectExpression(Context &context, ExpressionContext &exp
 	else if (expressionIdentifier == "forall"
 		|| expressionIdentifier == "when")
 	{
-		throwUnsupported(context.parser, expressionIdentifier);
+		warnUnsupported(context, expressionIdentifier);
+
+		return nullptr;
 	}
 	else
 		expression = parseEffectBodyExpressionContent(expressionIdentifier, context, expressionContext);
@@ -177,7 +184,9 @@ ExpressionPointer parseEffectBodyExpressionContent(const std::string &expression
 		|| expressionIdentifier == "increase"
 		|| expressionIdentifier == "decrease")
 	{
-		throwUnsupported(context.parser, expressionIdentifier);
+		warnUnsupported(context, expressionIdentifier);
+
+		return nullptr;
 	}
 
 	const auto &predicateDeclarations = expressionContext.domain.predicates();
diff --git a/src/plasp/pddl/InitialState.cpp b/src/plasp/pddl/InitialState.cpp
new file mode 100644
index 0000000..680f7ea
--- /dev/null
+++ b/src/plasp/pddl/InitialState.cpp
@@ -0,0 +1,63 @@
+#include <plasp/pddl/InitialState.h>
+
+#include <plasp/pddl/Context.h>
+#include <plasp/pddl/Identifier.h>
+#include <plasp/pddl/IO.h>
+#include <plasp/pddl/expressions/Predicate.h>
+#include <plasp/utils/ParserException.h>
+
+namespace plasp
+{
+namespace pddl
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// InitialState
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+inline void warnUnsupported(Context &context, const std::string &expressionIdentifier)
+{
+	context.logger.parserWarning(context.parser, "Expression type \"" + expressionIdentifier + "\" currently unsupported in this context");
+	skipSection(context.parser);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+std::unique_ptr<InitialState> InitialState::parseDeclaration(Context &context, const Problem &problem)
+{
+	auto initialState = std::make_unique<InitialState>(InitialState());
+
+	while (context.parser.currentCharacter() != ')')
+	{
+		context.parser.expect<std::string>("(");
+
+		ExpressionPointer expression;
+
+		const auto expressionIdentifier = context.parser.parseIdentifier(isIdentifier);
+
+		if (expressionIdentifier == "at"
+			|| expressionIdentifier == "="
+			|| expressionIdentifier == "not")
+		{
+			warnUnsupported(context, expressionIdentifier);
+
+			continue;
+		}
+
+		// If none of the above types apply, the content is a predicate over constants and objects
+		initialState->m_facts.emplace_back(expressions::Predicate::parse(expressionIdentifier, context, problem));
+
+		context.parser.expect<std::string>(")");
+
+		context.parser.skipWhiteSpace();
+	}
+
+	return initialState;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
diff --git a/src/plasp/pddl/Problem.cpp b/src/plasp/pddl/Problem.cpp
index a7835f8..35f7c14 100644
--- a/src/plasp/pddl/Problem.cpp
+++ b/src/plasp/pddl/Problem.cpp
@@ -29,7 +29,7 @@ Problem::Problem(Context &context, Domain &domain)
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void Problem::readPDDL()
+void Problem::parse()
 {
 	m_context.parser.expect<std::string>("(");
 	m_context.parser.expect<std::string>("define");
@@ -122,8 +122,9 @@ void Problem::parseSection()
 		parseRequirementSection();
 	else if (parser.probe<std::string>("objects"))
 		parseObjectSection();
-	else if (parser.probe<std::string>("init")
-		|| parser.probe<std::string>("goal")
+	else if (parser.probe<std::string>("init"))
+		parseInitialStateSection();
+	else if (parser.probe<std::string>("goal")
 		|| parser.probe<std::string>("constraints")
 		|| parser.probe<std::string>("metric")
 		|| parser.probe<std::string>("length"))
@@ -255,6 +256,33 @@ void Problem::parseObjectSection()
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+void Problem::parseInitialStateSection()
+{
+	m_initialState = InitialState::parseDeclaration(m_context, *this);
+
+	m_context.parser.expect<std::string>(")");
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+InitialState &Problem::initialState()
+{
+	BOOST_ASSERT(m_initialState);
+
+	return *m_initialState;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+const InitialState &Problem::initialState() const
+{
+	BOOST_ASSERT(m_initialState);
+
+	return *m_initialState;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 void Problem::checkConsistency()
 {
 }
diff --git a/src/plasp/pddl/expressions/Constant.cpp b/src/plasp/pddl/expressions/Constant.cpp
index a011713..9bfe0fc 100644
--- a/src/plasp/pddl/expressions/Constant.cpp
+++ b/src/plasp/pddl/expressions/Constant.cpp
@@ -134,24 +134,37 @@ void Constant::parseTypedDeclarations(Context &context, Problem &problem)
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-Constant *Constant::parseAndFind(Context &context, const ExpressionContext &expressionContext)
+Constant *Constant::parseAndFind(Context &context, const Domain &domain)
 {
 	context.parser.skipWhiteSpace();
 
 	const auto constantName = context.parser.parseIdentifier(isIdentifier);
 
-	auto *constant = parseAndFind(constantName, expressionContext.domain.constants());
+	auto *constant = parseAndFind(constantName, domain.constants());
+
+	if (constant != nullptr)
+		return constant;
+
+	throw utils::ParserException(context.parser, "Constant \"" + constantName + "\" used but never declared");
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+Constant *Constant::parseAndFind(Context &context, const Problem &problem)
+{
+	context.parser.skipWhiteSpace();
+
+	const auto constantName = context.parser.parseIdentifier(isIdentifier);
+
+	auto *constant = parseAndFind(constantName, problem.domain().constants());
 
 	if (constant)
 		return constant;
 
-	if (expressionContext.problem)
-	{
-		constant = parseAndFind(constantName, expressionContext.problem->objects());
+	constant = parseAndFind(constantName, problem.objects());
 
-		if (constant)
-			return constant;
-	}
+	if (constant)
+		return constant;
 
 	throw utils::ParserException(context.parser, "Constant \"" + constantName + "\" used but never declared");
 }
diff --git a/src/plasp/pddl/expressions/InitialState.cpp b/src/plasp/pddl/expressions/InitialState.cpp
deleted file mode 100644
index 3d85d3f..0000000
--- a/src/plasp/pddl/expressions/InitialState.cpp
+++ /dev/null
@@ -1,54 +0,0 @@
-#include <plasp/pddl/expressions/Type.h>
-
-#include <plasp/pddl/Context.h>
-#include <plasp/pddl/Identifier.h>
-#include <plasp/pddl/expressions/Predicate.h>
-#include <plasp/utils/IO.h>
-#include <plasp/utils/ParserException.h>
-
-namespace plasp
-{
-namespace pddl
-{
-namespace expressions
-{
-
-////////////////////////////////////////////////////////////////////////////////////////////////////
-//
-// InitialState
-//
-////////////////////////////////////////////////////////////////////////////////////////////////////
-
-void throwUnsupported(const utils::Parser &parser, const std::string &expressionIdentifier)
-{
-	throw utils::ParserException(parser, "Expression type \"" + expressionIdentifier + "\" currently unsupported in this context");
-}
-
-////////////////////////////////////////////////////////////////////////////////////////////////////
-
-ExpressionPointer parseInitialState(Context &context)
-{
-	context.parser.expect<std::string>("(");
-
-	const auto expressionIdentifier = context.parser.parseIdentifier(isIdentifier);
-
-	ExpressionPointer expression;
-
-	if (expressionIdentifier == "at"
-		|| expressionIdentifier == "=")
-	{
-		throwUnsupported(context.parser, expressionIdentifier);
-	}
-
-	// TODO: implement predicate parsing
-
-	context.parser.expect<std::string>(")");
-
-	return expression;
-}
-
-////////////////////////////////////////////////////////////////////////////////////////////////////
-
-}
-}
-}
diff --git a/src/plasp/pddl/expressions/Predicate.cpp b/src/plasp/pddl/expressions/Predicate.cpp
index 73f9bdf..1e3c27a 100644
--- a/src/plasp/pddl/expressions/Predicate.cpp
+++ b/src/plasp/pddl/expressions/Predicate.cpp
@@ -51,7 +51,9 @@ PredicatePointer Predicate::parse(std::string name, Context &context,
 		// Parse constants
 		else
 		{
-			const auto *constant = Constant::parseAndFind(context, expressionContext);
+			const auto *constant = (expressionContext.problem == nullptr)
+				? Constant::parseAndFind(context, expressionContext.domain)
+				: Constant::parseAndFind(context, *expressionContext.problem);
 			auto constantReference = std::make_unique<Reference<Constant>>(constant);
 			predicate->m_arguments.emplace_back(std::move(constantReference));
 		}
@@ -66,6 +68,32 @@ PredicatePointer Predicate::parse(std::string name, Context &context,
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+PredicatePointer Predicate::parse(std::string name, Context &context, const Problem &problem)
+{
+	auto predicate = std::make_unique<Predicate>(Predicate());
+
+	predicate->m_name = name;
+
+	context.parser.skipWhiteSpace();
+
+	while (context.parser.currentCharacter() != ')')
+	{
+		if (context.parser.currentCharacter() == '?')
+			throw utils::ParserException(context.parser, "Variables not allowed in this context");
+
+		// Parse objects and constants
+		const auto *constant = Constant::parseAndFind(context, problem);
+		auto constantReference = std::make_unique<Reference<Constant>>(constant);
+		predicate->m_arguments.emplace_back(std::move(constantReference));
+	}
+
+	// TODO: check that signature matches one of the declared ones
+
+	return predicate;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 void Predicate::accept(plasp::pddl::ExpressionVisitor &expressionVisitor) const
 {
 	expressionVisitor.visit(*this);