The increase in ‘atypical’ or precarious forms of work, including part-time, temporary or agency, contracted-out, posted, dependent self-employed and undocumented work, has created one of the major challenges facing trade unions in Europe today. Indeed, the ‘atypical’ has become more and more ‘typical’ in a number of European countries, particularly among women and younger workers. The rise in atypical forms of work calls for changes in the way trade unions develop strategies, policies and structures and presents a challenge to their traditional ways of thinking and organising. This article begins with the definition of atypical work and a general overview of the literature on the subject before moving on to the nature of the challenge it creates for trade unions in Europe and an overview of their responses, drawing on preliminary findings from a three-year research project in unions in 10 European countries. The article concludes that while unions have made a great deal of progress in addressing the concerns of atypical workers, they will have to make substantial changes to their structures, thinking and way of operating in order to be fully able to respond to the challenge of this growing form of work.