This book benefitted greatly from the support of Jürgen Renn, who not only co-organised and funded (via the MPIWG) two highly successful workshops on the early history of quantum gravity (at Pasadena in 2010 and Berlin in 2011), but also helped fund several research projects closely related to this book. We wish to also acknowledge Diana Kormos-Buchwald and Tilman Sauer (now University of Mainz), of the Einstein Papers Project, who were also responsible for the organisation of the Pasadena workshop. The participants in those workshop sessions deserve thanks for their probing analyses of several of the papers that appear in this volume. We would also like to thank Urte Brauckmann of the MPIWG library for her invaluable help in procuring the reproduction rights to the papers. Dean Rickles would also like to thank the Australian Research Council for its support of his historical research via a Future Fellowship: FT130100466.