diff --git a/lib/pddlparse/include/pddlparse/ASTForward.h b/lib/pddlparse/include/pddlparse/ASTForward.h
index c14d06e..6a520b5 100644
--- a/lib/pddlparse/include/pddlparse/ASTForward.h
+++ b/lib/pddlparse/include/pddlparse/ASTForward.h
@@ -173,6 +173,24 @@ using Preconditions = std::vector<Precondition>;
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
+class ConditionalEffect;
+
+namespace detail
+{
+using ConditionalEffectT = Variant<
+	AtomicFormula,
+	AndPointer<ConditionalEffect>,
+	NotPointer<ConditionalEffect>,
+	UnsupportedPointer>;
+}
+
+class ConditionalEffect : public detail::ConditionalEffectT
+{
+	using detail::ConditionalEffectT::ConditionalEffectT;
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 class Effect;
 
 namespace detail
@@ -182,7 +200,7 @@ using EffectT = Variant<
 	AndPointer<Effect>,
 	ForAllPointer<Effect>,
 	NotPointer<Effect>,
-	WhenPointer<Precondition, Effect>,
+	WhenPointer<Precondition, ConditionalEffect>,
 	UnsupportedPointer>;
 }
 
diff --git a/lib/pddlparse/include/pddlparse/detail/parsing/Effect.h b/lib/pddlparse/include/pddlparse/detail/parsing/Effect.h
new file mode 100644
index 0000000..5e67f22
--- /dev/null
+++ b/lib/pddlparse/include/pddlparse/detail/parsing/Effect.h
@@ -0,0 +1,27 @@
+#ifndef __PDDL_PARSE__DETAIL__PARSING__EFFECT_H
+#define __PDDL_PARSE__DETAIL__PARSING__EFFECT_H
+
+#include <pddlparse/ASTForward.h>
+#include <pddlparse/Context.h>
+#include <pddlparse/detail/ASTContext.h>
+#include <pddlparse/detail/VariableStack.h>
+
+namespace pddl
+{
+namespace detail
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// Effect
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+std::experimental::optional<ast::Effect> parseEffect(Context &context, ASTContext &astContext, VariableStack &variableStack);
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
+
+#endif
diff --git a/lib/pddlparse/include/pddlparse/detail/parsing/Precondition.h b/lib/pddlparse/include/pddlparse/detail/parsing/Precondition.h
index fb27a86..f6a99da 100644
--- a/lib/pddlparse/include/pddlparse/detail/parsing/Precondition.h
+++ b/lib/pddlparse/include/pddlparse/detail/parsing/Precondition.h
@@ -18,6 +18,7 @@ namespace detail
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 std::experimental::optional<ast::Precondition> parsePrecondition(Context &context, ASTContext &astContext, VariableStack &variableStack);
+std::experimental::optional<ast::Precondition> parsePreconditionBody(Context &context, ASTContext &astContext, VariableStack &variableStack);
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
diff --git a/lib/pddlparse/src/pddlparse/detail/parsing/Action.cpp b/lib/pddlparse/src/pddlparse/detail/parsing/Action.cpp
index 5f3fbc8..8051ab9 100644
--- a/lib/pddlparse/src/pddlparse/detail/parsing/Action.cpp
+++ b/lib/pddlparse/src/pddlparse/detail/parsing/Action.cpp
@@ -3,8 +3,8 @@
 #include <pddlparse/AST.h>
 #include <pddlparse/detail/ASTContext.h>
 #include <pddlparse/detail/VariableStack.h>
+#include <pddlparse/detail/parsing/Effect.h>
 #include <pddlparse/detail/parsing/Precondition.h>
-// TODO: remove
 #include <pddlparse/detail/parsing/Utils.h>
 #include <pddlparse/detail/parsing/VariableDeclaration.h>
 
@@ -159,26 +159,18 @@ void ActionParser::parsePreconditionSection(ast::Action &action)
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void ActionParser::parseEffectSection(ast::Action &)
+void ActionParser::parseEffectSection(ast::Action &action)
 {
 	auto &tokenizer = m_context.tokenizer;
 
 	tokenizer.expect<std::string>(":effect");
-	tokenizer.expect<std::string>("(");
 
-	m_context.warningCallback(tokenizer.location(), "effect parser under construction, section is currently ignored");
+	VariableStack variableStack;
+	variableStack.push(&action.parameters);
 
-	// TODO: reimplement
-	//VariableStack variableStack;
-	//variableStack.push(&action.parameters);
+	ASTContext astContext(m_domain);
 
-	//ASTContext astContext(m_domain);
-
-	//action.precondition = parseEffect(m_context, astContext, variableStack);
-
-	//tokenizer.expect<std::string>(")");
-
-	skipSection(tokenizer);
+	action.effect = parseEffect(m_context, astContext, variableStack);
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/lib/pddlparse/src/pddlparse/detail/parsing/Effect.cpp b/lib/pddlparse/src/pddlparse/detail/parsing/Effect.cpp
new file mode 100644
index 0000000..d8b0f0e
--- /dev/null
+++ b/lib/pddlparse/src/pddlparse/detail/parsing/Effect.cpp
@@ -0,0 +1,154 @@
+#include <pddlparse/detail/parsing/Effect.h>
+
+#include <pddlparse/AST.h>
+#include <pddlparse/detail/parsing/Expressions.h>
+#include <pddlparse/detail/parsing/Precondition.h>
+#include <pddlparse/detail/parsing/Predicate.h>
+#include <pddlparse/detail/parsing/Unsupported.h>
+#include <pddlparse/detail/parsing/Utils.h>
+
+namespace pddl
+{
+namespace detail
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// Effect
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+std::experimental::optional<ast::Effect> parseEffectBody(Context &context, ASTContext &astContext, VariableStack &variableStack);
+std::experimental::optional<ast::ConditionalEffect> parseConditionalEffect(Context &context, ASTContext &astContext, VariableStack &variableStack);
+std::experimental::optional<ast::ConditionalEffect> parseConditionalEffectBody(Context &context, ASTContext &astContext, VariableStack &variableStack);
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+std::experimental::optional<ast::Effect> parseEffect(Context &context, ASTContext &astContext, VariableStack &variableStack)
+{
+	auto &tokenizer = context.tokenizer;
+
+	tokenizer.skipWhiteSpace();
+
+	std::experimental::optional<ast::Effect> effect;
+
+	if ((effect = parseAnd<ast::Effect>(context, astContext, variableStack, parseEffect))
+	    || (effect = parseForAll<ast::Effect>(context, astContext, variableStack, parseEffect))
+	    || (effect = parseWhen<ast::Precondition, ast::ConditionalEffect>(context, astContext, variableStack, parsePreconditionBody, parseConditionalEffect)))
+	{
+		return std::move(effect.value());
+	}
+
+	return parseEffectBody(context, astContext, variableStack);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+std::experimental::optional<ast::Effect> parseEffectBody(Context &context, ASTContext &astContext, VariableStack &variableStack)
+{
+	auto &tokenizer = context.tokenizer;
+
+	tokenizer.skipWhiteSpace();
+
+	// Test unsupported expressions first
+	const auto position = tokenizer.position();
+
+	tokenizer.expect<std::string>("(");
+	tokenizer.skipWhiteSpace();
+
+	const auto expressionIdentifierPosition = tokenizer.position();
+
+	if (tokenizer.testIdentifierAndReturn("=")
+		|| tokenizer.testIdentifierAndReturn("assign")
+		|| tokenizer.testIdentifierAndReturn("scale-up")
+		|| tokenizer.testIdentifierAndReturn("scale-down")
+		|| tokenizer.testIdentifierAndReturn("increase")
+		|| tokenizer.testIdentifierAndReturn("decrease"))
+	{
+		tokenizer.seek(position);
+		return parseUnsupported(context);
+	}
+
+	tokenizer.seek(position);
+
+	// Now, test supported expressions
+	std::experimental::optional<ast::Effect> effect;
+
+	if ((effect = parseNot<ast::Effect>(context, astContext, variableStack, parsePredicate))
+		|| (effect = parsePredicate(context, astContext, variableStack)))
+	{
+		return std::move(effect.value());
+	}
+
+	tokenizer.seek(expressionIdentifierPosition);
+	const auto expressionIdentifier = tokenizer.getIdentifier();
+
+	tokenizer.seek(position);
+	throw tokenize::TokenizerException(tokenizer.location(), "expression type “" + expressionIdentifier + "” unknown or not allowed in effect body");
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+std::experimental::optional<ast::ConditionalEffect> parseConditionalEffect(Context &context, ASTContext &astContext, VariableStack &variableStack)
+{
+	auto &tokenizer = context.tokenizer;
+
+	tokenizer.skipWhiteSpace();
+
+	std::experimental::optional<ast::ConditionalEffect> conditionalEffect;
+
+	if ((conditionalEffect = parseAnd<ast::ConditionalEffect>(context, astContext, variableStack, parseConditionalEffectBody)))
+		return std::move(conditionalEffect.value());
+
+	return parseConditionalEffectBody(context, astContext, variableStack);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+std::experimental::optional<ast::ConditionalEffect> parseConditionalEffectBody(Context &context, ASTContext &astContext, VariableStack &variableStack)
+{
+	auto &tokenizer = context.tokenizer;
+
+	tokenizer.skipWhiteSpace();
+
+	// Test unsupported expressions first
+	const auto position = tokenizer.position();
+
+	tokenizer.expect<std::string>("(");
+	tokenizer.skipWhiteSpace();
+
+	const auto expressionIdentifierPosition = tokenizer.position();
+
+	if (tokenizer.testIdentifierAndReturn("=")
+		|| tokenizer.testIdentifierAndReturn("assign")
+		|| tokenizer.testIdentifierAndReturn("scale-up")
+		|| tokenizer.testIdentifierAndReturn("scale-down")
+		|| tokenizer.testIdentifierAndReturn("increase")
+		|| tokenizer.testIdentifierAndReturn("decrease"))
+	{
+		tokenizer.seek(position);
+		return parseUnsupported(context);
+	}
+
+	tokenizer.seek(position);
+
+	// Now, test supported expressions
+	std::experimental::optional<ast::ConditionalEffect> conditionalEffect;
+
+	if ((conditionalEffect = parseNot<ast::ConditionalEffect>(context, astContext, variableStack, parsePredicate))
+		|| (conditionalEffect = parsePredicate(context, astContext, variableStack)))
+	{
+		return std::move(conditionalEffect.value());
+	}
+
+	tokenizer.seek(expressionIdentifierPosition);
+	const auto expressionIdentifier = tokenizer.getIdentifier();
+
+	tokenizer.seek(position);
+	throw tokenize::TokenizerException(tokenizer.location(), "expression type “" + expressionIdentifier + "” unknown or not allowed in conditional effect body");
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
diff --git a/lib/pddlparse/src/pddlparse/detail/parsing/Precondition.cpp b/lib/pddlparse/src/pddlparse/detail/parsing/Precondition.cpp
index 493a02d..dd165a3 100644
--- a/lib/pddlparse/src/pddlparse/detail/parsing/Precondition.cpp
+++ b/lib/pddlparse/src/pddlparse/detail/parsing/Precondition.cpp
@@ -17,24 +17,13 @@ namespace detail
 //
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-std::experimental::optional<ast::Precondition> parsePreconditionBody(Context &context, ASTContext &astContext, VariableStack &variableStack);
-
-////////////////////////////////////////////////////////////////////////////////////////////////////
-
 std::experimental::optional<ast::Precondition> parsePrecondition(Context &context, ASTContext &astContext, VariableStack &variableStack)
 {
 	auto &tokenizer = context.tokenizer;
 
 	tokenizer.skipWhiteSpace();
 
-	std::experimental::optional<ast::Precondition> precondition;
-
-	if ((precondition = parseAnd<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
-	    || (precondition = parseForAll<ast::Precondition>(context, astContext, variableStack, parsePrecondition)))
-	{
-		return std::move(precondition.value());
-	}
-
+	// Test unsupported expressions first
 	const auto position = tokenizer.position();
 
 	tokenizer.expect<std::string>("(");
@@ -45,6 +34,17 @@ std::experimental::optional<ast::Precondition> parsePrecondition(Context &contex
 		return parseUnsupported(context);
 	}
 
+	tokenizer.seek(position);
+
+	// Now, test supported expressions
+	std::experimental::optional<ast::Precondition> precondition;
+
+	if ((precondition = parseAnd<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
+	    || (precondition = parseForAll<ast::Precondition>(context, astContext, variableStack, parsePrecondition)))
+	{
+		return std::move(precondition.value());
+	}
+
 	tokenizer.seek(position);
 	return parsePreconditionBody(context, astContext, variableStack);
 }
@@ -57,19 +57,7 @@ std::experimental::optional<ast::Precondition> parsePreconditionBody(Context &co
 
 	tokenizer.skipWhiteSpace();
 
-	std::experimental::optional<ast::Precondition> precondition;
-
-	if ((precondition = parseAnd<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
-	    || (precondition = parseOr<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
-	    || (precondition = parseExists<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
-	    || (precondition = parseForAll<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
-		|| (precondition = parseNot<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
-	    || (precondition = parseImply<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
-	    || (precondition = parsePredicate(context, astContext, variableStack)))
-	{
-		return std::move(precondition.value());
-	}
-
+	// Test unsupported expressions first
 	const auto position = tokenizer.position();
 
 	tokenizer.expect<std::string>("(");
@@ -93,11 +81,27 @@ std::experimental::optional<ast::Precondition> parsePreconditionBody(Context &co
 		return parseUnsupported(context);
 	}
 
+	tokenizer.seek(position);
+
+	// Now, test supported expressions
+	std::experimental::optional<ast::Precondition> precondition;
+
+	if ((precondition = parseAnd<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
+	    || (precondition = parseOr<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
+	    || (precondition = parseExists<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
+	    || (precondition = parseForAll<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
+		|| (precondition = parseNot<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
+	    || (precondition = parseImply<ast::Precondition>(context, astContext, variableStack, parsePrecondition))
+	    || (precondition = parsePredicate(context, astContext, variableStack)))
+	{
+		return std::move(precondition.value());
+	}
+
 	tokenizer.seek(expressionIdentifierPosition);
 	const auto expressionIdentifier = tokenizer.getIdentifier();
 
 	tokenizer.seek(position);
-	throw tokenize::TokenizerException(tokenizer.location(), "expression type “" + expressionIdentifier + "” unknown or not allowed in this context");
+	throw tokenize::TokenizerException(tokenizer.location(), "expression type “" + expressionIdentifier + "” unknown or not allowed in precondition body");
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////