Informers are generally reviled. After all, 'snitches get stitches.' Informers who report to repressive regimes are particularly disdained. While informers may themselves be victims enlisted by the state, their actions cause other individuals to suffer significant harm. Informers, then, are central to the proliferation of endemic human rights abuses. Yet, little is known about exactly why ordinary people end up informing on--at times betraying--other people to state authorities. Through a case-study of Communist Czechoslovakia (1945-1989) that draws from secret police archives, oral histories, and a broad gamut of secondary sources, this book unearths what fuels informers to speak to the secret police in repressive times and considers how transitional justice should approach informers once repression ends. This book unravels the complex drivers behind informing and the dynamics of societal reactions to informing. It explores the agency of both informers and secret police officers. By presenting informers up close, and the relationships between informers and secret police officers in high resolution, this book centres the role of emotions in informer motivations and underscores the value of dignity and reconciliation in transitional reconstruction. This book also leverages research from informing in repressive states to better understand informing in so-called liberal democratic states, which, after all, also rely on informers to maintain law and preserve order.