Drawing from political science and organisational studies, but also from social movement analysis, this chapter examines the current terms of the debate on the future of Labour organising and tracks the emergence of hybrid forms of political parties with emphasis now placed on social movement activities alongside traditional election campaigning. This process of ‘movementisation’ is couched by some in optimistic terms as a way to reconnect the party with civil society, while others point on the contrary to the dangers such an evolution may entail, arguing that radicalisation will alienate the party further from the interests of the wider electorate. The analysis starts with some methodological considerations, continues with a presentation of Labour supporting groups and movements, with particular focus on the most recent one – Momentum – and then leads to an appraisal of the impact which this process is having on the structure and mobilising power of the Labour party.