This book grew out of a need to have a set of easily accessible notes that introduced the basic techniques used in modern research on scattering amplitudes. In addition to the key tools, such a review should collect some of the small results and intuitions the authors had acquired from their work in the field and which had not previously been exposed in the literature. As the authors quickly realized, such an introduction would bring the reader only part of the way towards some of the most exciting topics in the field, so they decided to add “a little extra” material. While doing so – and this took quite a while – the authors remained in full and complete denial about writing a book. It was only at the end of the process that they faced their worst fears: the review was becoming a book. You now hold the result in your hands. Because the authors were not writing a book, they actually thoroughly enjoyed the work. Their hope is that you will enjoy it too and that you will find it useful.

It is a pleasure to thank our friends and collaborators who have worked with us and helped us learn the subject of scattering amplitudes: Ratin Akhoury, Nima Arkani-Hamed, Zvi Bern, Freddy Cachazo, John Joseph Carrasco, Simon Caron-Huot, Tim Cohen, Scott Davies, Tristan Dennen, Lance Dixon, Dan Freedman, David Kosower, Johannes Henn, Harald Ita, Henrik Johansson, Michael Kiermaier, Sangmin Lee, Arthur Lipstein, Thomas Lam, David McGady, Timothy Olson, Cheng Peng, Jan Plefka, Radu Roiban, Mark Srednicki, Warren Siegel, David Speyer, and Jaroslav Trnka. H.E. is grateful for the hospitality offered by Stanford/SLAC during her visit in February/March 2013 and KITP/UCSB during January–March 2014.

A few people have suffered early drafts of this book and we are indebted to them for their helpful comments/suggestions/corrections: Cindy Keeler, Timothy Olson, Sam Roland, David Speyer, Sri Suresh, Jonathan Walsh, and John Ware.