diff --git a/include/plasp/pddl/expressions/NotExpression.h b/include/plasp/pddl/expressions/NotExpression.h
new file mode 100644
index 0000000..b2a8f84
--- /dev/null
+++ b/include/plasp/pddl/expressions/NotExpression.h
@@ -0,0 +1,58 @@
+#ifndef __PLASP__PDDL__EXPRESSION__NOT_EXPRESSION_H
+#define __PLASP__PDDL__EXPRESSION__NOT_EXPRESSION_H
+
+#include <plasp/pddl/Expression.h>
+#include <plasp/pddl/Predicate.h>
+
+namespace plasp
+{
+namespace pddl
+{
+namespace expressions
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// NotExpression
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class NotExpression: public Expression
+{
+	public:
+		template<typename ExpressionParser>
+		static std::unique_ptr<NotExpression> parse(utils::Parser &parser, Context &context, const Variables &parameters, ExpressionParser parseExpression);
+
+	public:
+		void accept(ExpressionVisitor &expressionVisitor) const override;
+
+		const Expression &argument();
+
+	private:
+		NotExpression() = default;
+
+		std::unique_ptr<Expression> m_argument;
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+template<typename ExpressionParser>
+std::unique_ptr<NotExpression> NotExpression::parse(utils::Parser &parser, Context &context, const Variables &parameters, ExpressionParser parseExpression)
+{
+	auto expression = std::make_unique<NotExpression>(NotExpression());
+
+	parser.skipWhiteSpace();
+
+	// Parse argument
+	expression->m_argument = parseExpression(parser, context, parameters);
+
+	return expression;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
+}
+
+#endif
diff --git a/src/plasp/pddl/Action.cpp b/src/plasp/pddl/Action.cpp
index 3f96c0c..d2a975a 100644
--- a/src/plasp/pddl/Action.cpp
+++ b/src/plasp/pddl/Action.cpp
@@ -57,8 +57,6 @@ Action &Action::parseDeclaration(utils::Parser &parser, Context &context)
 			action->m_effect = parseEffectExpression(parser, context, action->m_parameters);
 	}
 
-	parser.expect<std::string>(")");
-
 	// Store new action
 	context.actions.emplace_back(std::move(action));
 
diff --git a/src/plasp/pddl/Expression.cpp b/src/plasp/pddl/Expression.cpp
index 135b4e4..44de3b5 100644
--- a/src/plasp/pddl/Expression.cpp
+++ b/src/plasp/pddl/Expression.cpp
@@ -3,6 +3,7 @@
 #include <plasp/pddl/Context.h>
 #include <plasp/pddl/Identifier.h>
 #include <plasp/pddl/expressions/AndExpression.h>
+#include <plasp/pddl/expressions/NotExpression.h>
 #include <plasp/pddl/expressions/OrExpression.h>
 #include <plasp/pddl/expressions/PredicateExpression.h>
 #include <plasp/utils/ParserException.h>
@@ -20,6 +21,7 @@ namespace pddl
 
 std::unique_ptr<Expression> parseExpressionContent(const std::string &expressionIdentifier, utils::Parser &parser, Context &context, const Variables &parameters);
 std::unique_ptr<Expression> parseEffectBodyExpressionContent(const std::string &expressionIdentifier, utils::Parser &parser, Context &context, const Variables &parameters);
+std::unique_ptr<Expression> parsePredicateExpression(utils::Parser &parser, Context &context, const Variables &parameters);
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -32,8 +34,6 @@ void throwUnsupported(const utils::Parser &parser, const std::string &expression
 
 std::unique_ptr<Expression> parsePreconditionExpression(utils::Parser &parser, Context &context, const Variables &parameters)
 {
-	parser.skipWhiteSpace();
-
 	parser.expect<std::string>("(");
 
 	const auto expressionIdentifier = parser.parseIdentifier(isIdentifier);
@@ -59,8 +59,6 @@ std::unique_ptr<Expression> parsePreconditionExpression(utils::Parser &parser, C
 
 std::unique_ptr<Expression> parseExpression(utils::Parser &parser, Context &context, const Variables &parameters)
 {
-	parser.skipWhiteSpace();
-
 	parser.expect<std::string>("(");
 
 	const auto expressionIdentifier = parser.parseIdentifier(isIdentifier);
@@ -84,8 +82,9 @@ std::unique_ptr<Expression> parseExpressionContent(const std::string &expression
 		expression = expressions::AndExpression::parse(parser, context, parameters, parseExpression);
 	else if (expressionIdentifier == "or")
 		expression = expressions::OrExpression::parse(parser, context, parameters, parseExpression);
-	else if (expressionIdentifier == "not"
-		|| expressionIdentifier == "imply"
+	else if (expressionIdentifier == "not")
+		expression = expressions::NotExpression::parse(parser, context, parameters, parseExpression);
+	else if (expressionIdentifier == "imply"
 		|| expressionIdentifier == "exists"
 		|| expressionIdentifier == "forall"
 		|| expressionIdentifier == "-"
@@ -125,14 +124,10 @@ std::unique_ptr<Expression> parseExpressionContent(const std::string &expression
 
 std::unique_ptr<Expression> parseEffectExpression(utils::Parser &parser, Context &context, const Variables &parameters)
 {
-	parser.skipWhiteSpace();
-
 	parser.expect<std::string>("(");
 
 	const auto expressionIdentifier = parser.parseIdentifier(isIdentifier);
 
-	std::cout << "Parsing effect expression " << expressionIdentifier << std::endl;
-
 	std::unique_ptr<Expression> expression;
 
 	if (expressionIdentifier == "and")
@@ -154,12 +149,11 @@ std::unique_ptr<Expression> parseEffectExpression(utils::Parser &parser, Context
 
 std::unique_ptr<Expression> parseEffectBodyExpressionContent(const std::string &expressionIdentifier, utils::Parser &parser, Context &context, const Variables &parameters)
 {
-	parser.skipWhiteSpace();
-
 	std::unique_ptr<Expression> expression;
 
-	if (expressionIdentifier == "not"
-		|| expressionIdentifier == "="
+	if (expressionIdentifier == "not")
+		expression = expressions::NotExpression::parse(parser, context, parameters, parsePredicateExpression);
+	else if (expressionIdentifier == "="
 		|| expressionIdentifier == "assign"
 		|| expressionIdentifier == "scale-up"
 		|| expressionIdentifier == "scale-down"
@@ -189,5 +183,33 @@ std::unique_ptr<Expression> parseEffectBodyExpressionContent(const std::string &
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+std::unique_ptr<Expression> parsePredicateExpression(utils::Parser &parser, Context &context, const Variables &parameters)
+{
+	parser.expect<std::string>("(");
+
+	const auto predicateName = parser.parseIdentifier(isIdentifier);
+
+	std::unique_ptr<Expression> expression;
+
+	// Check if predicate with that name exists
+	const auto match = std::find_if(context.predicates.cbegin(), context.predicates.cend(),
+		[&](const auto &predicate)
+		{
+			return predicate->name() == predicateName;
+		});
+
+	// If predicate exists, parse it
+	if (match == context.predicates.cend())
+		throw utils::ParserException(parser.row(), parser.column(), "Unknown predicate \"" + predicateName + "\"");
+
+	expression = expressions::PredicateExpression::parse(predicateName, parser, context, parameters);
+
+	parser.expect<std::string>(")");
+
+	return expression;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 }
 }
diff --git a/src/plasp/pddl/expressions/NotExpression.cpp b/src/plasp/pddl/expressions/NotExpression.cpp
new file mode 100644
index 0000000..1f880b8
--- /dev/null
+++ b/src/plasp/pddl/expressions/NotExpression.cpp
@@ -0,0 +1,27 @@
+#include <plasp/pddl/expressions/NotExpression.h>
+
+#include <plasp/pddl/ExpressionVisitor.h>
+
+namespace plasp
+{
+namespace pddl
+{
+namespace expressions
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// NotExpression
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+void NotExpression::accept(plasp::pddl::ExpressionVisitor &expressionVisitor) const
+{
+	expressionVisitor.visit(*this);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
+}