Postfunctionalism is a theory of European integration put forward by Liesbet Hooghe and Gary Marks in 2008, in opposition to the previous two main theories of European integration Neofunctionalism and Intergovernmentalism, as they could not explain critical aspects of European integration such as referenda and European issues becoming a part of national politics.
Hence, the preferences of political parties and national publics now play a crucial role in shaping the EU's politics and integration.
[1] In 2019, Hooghe and Marks advocated for a pluralist approach to theories of European integration.
On this account, Neofunctionalism, Intergovernmentalism and Postfunctionalism are not competing approaches but rather they provided lenses that discipline our thinking about "the behavior of key actors, the arenas in which they act, and the causal mechanisms that connect their actions to institutional outcomes".
[2] Each approach offers a distinct analysis of EU crises where "the Eurocrisis, the migration crisis, Brexit, and illiberalism can be viewed as episodes of intergovernmental bargaining, path-dependent spillovers, and ideological conflict".