This edited volume is devoted to the analysis of practices of transnational solidarity in response to the various crises affecting Europe, especially the economic and refugee crises. Its aim is to present new insights into existing informal groups, at the grassroots, geared at furthering transnational solidarity in three thematic areas (disability, unemployment and immigration) and builds on extensive fieldwork in eight European countries (Denmark, France, Germany, Greece, Italy, Poland, Switzerland and the UK). The introductory chapter provides an overview of the topic and the related research, discusses conceptual and methodological issues, and presents the structure of the book. It argues that the transnational solidarity work of citizen groups and organisations is strongly shaped by the socio-economic and political context in which they operate, by the action repertoires they promote, the networks of cooperation they are involved in and the experiences and lessons learned by engaged citizens and activists. It argues that in spite of apparent differences tied to contexts, there are a number of similarities in regard to the way transnationally oriented solidarity groups and organisations respond to societal challenges.