What makes a neo-Nazi become a convinced anti-fascist or a radical left-winger become a devout Salafist? How do they manage to fit into their new environment and gain acceptance as a former enemy? The people featured in this book made highly puzzling journeys, first venturing into extremist milieus and then deciding to switch to the opposite side. By using their extraordinary life-stories and their own narratives, this book provides the first in-depth analysis of how and why people move between seemingly opposing extremist environments that can sometimes overlap and influence each other. It aims to understand how these extremists manage to convince their new group that they can be trusted, which also allows us to dive deep into the psychology of extremism and terrorism. This fascinating work will be of immense value to those studying radicalization and counter-radicalization in terrorism studies, social psychology and political science.

‘A tour de force, offering an original take on a neglected aspect of extremist radicalization: the strange phenomenon of extremist side-switchers. Koehler’s gripping narrative account of defectors who migrate across extremist groups and ideologies is both absorbing and trailblazing, shedding important new light on critical vulnerabilities during de-radicalization and disengagement processes.’

Cynthia Miller-Idriss - Professor in the School of Public Affairs and the School of Education, American University, USA

‘Side-switchers are a new direction in radicalization research! The stories are fascinating, each one a psychological puzzle that challenges dissonance theory, rational choice theory, loss aversion theory, the sunk costs fallacy, and the importance of ideology in political radicalization.’

Clark R. McCauley - Professor Emeritus of Psychology, Bryn Mawr College, USA

‘A trailblazing text, painstakingly researched and exceptionally well organized. Koehler’s analysis seamlessly merges theory with real-world case studies of side-switching, indicative of his roots as both a P/CVE scholar and a practitioner that is second to none.’

Michael J. Williams - Ph.D., founding member, The Science of P/CVE

‘A reader could find no better expert than Daniel Koehler to develop an in-depth knowledge about the dynamics of violent extremism. With From Traitor to Zealot, Koehler adds to his impressive catalog of must-reads concerning the ways that individuals enter and leave extremist groups. This book addresses a critical gap in our understanding of why extremists ‘switch sides,’ and will undoubtedly help researchers and practitioners recognize that the path into and out of terrorism is never a straight line.’

Kurt Braddock - Assistant Professor in the School of Communication, American University, USA

‘How can some extremist ‘true believers’ - radical left-, right-wingers or Islamists - change sides and switch to the opposite ‘truth,’ betraying their original cause and colleagues? Such conversions are rare; but by focusing on exceptions, as Daniel Koehler does in two dozen fascinating biographic portraits of defectors, he throws new light on the psychology of radicalization and the difficulties of returning to mainstream society once someone gets caught up in narrow-minded subcultures. A truly original study.’

Alex P. Schmid - Editor-in-Chief, Perspectives on Terrorism

‘Theoretically rich and storyline-driven, From Traitor to Zealot is an instant classic of the field. Koehler shines a bright light on a counter-intuitive phenomenon many are anecdotally aware of - extremists who switch sides - but the book will surprise many by outlining how common, complex and dramatical the process is.’

Paul Gill - Professor of Security and Crime Science, University College London, UK