Challenging Ideas is a selection of articles which address the intersections between theory and empirical research. In general, the contributions to the volume focus on how imaginations of the temporal relationship between past and present might inform theory as well as empirical research. It is divided into two parts, the first of which, Memory, looks at the memory turn in the discipline of history, and includes investigations into the relationship between past and present in the working through of trauma and reflections on the relationship between media memory, collective memory and trauma. The second part of the volume, History looks at the intersections between social science, political theory and the writing of history. This section includes reflections on how the historian's archival work might inform the construction of social and political theory and explorations of the temporal relationship between past and present at work in the archives. The contributions to this volume encourage historically oriented scholars to approach their work with an active interest in disciplines close to their topic and a reflexive attentiveness to the broader power relations within which they work. They offer different perspectives on the intrinsic relationship between past and present at work in the interactions between theory and empirical research, and thereby give impetus to challenging ideas and to the challenging of ideas in the social sciences and in the humanities.