This article reassesses the debate around the meaning of ‘libertarian communism’ within the Spanish anarcho-syndicalist movement in the years prior to and during the Civil War. Drawing on recent historical and theoretical literature that argues for a non-pejorative and analytical understanding of utopia, it brings renewed attention to this aspect of Spanish anarcho-syndicalism. The article focuses on the proposals for a definition of libertarian communism that were debated in the run up to and during the National Confederation of Labour’s (CNT) Zaragoza Congress in May 1936. It argues that a utopian imagination was central to the movement’s self-understanding and concrete achievements, and not confined to its more idealist currents.