Trotskyists have always attached enormous importance to work inside the trade union movement because of the belief that it represents the most organized and class conscious section of the working class. This chapter rehearses the theoretical rationale for trade union activity and the expectations of Trotskyists about their engagement in workers' struggles against employers and the state before describing the parameters of Trotskyist activity and influence within the contemporary trade union movement. It draws on the party/sect/social movement framework to identify and analyses two major contradictions inherent in Trotskyist trade union work. Competition between Trotskyist groups within the trade union movement is not a recent phenomenon but can be traced back to the 1960s and the struggle to achieve hegemony on the revolutionary left. However the problems of Trotskyist trade union work are not simply organizational but are rooted in an impoverished theory of class consciousness.