History shows us that peoples' movements are more likely to suc­ceed when they have unity among supporters, widespread participa­tion, strategic planning, and non­violent discipline. Unsurprisingly, movement opponents use agent provocateurs-fake activists work­ing undercover-to behave in counterproductive ways that undermine these four keys to success. Drawing from international exam­ples, and an in-depth case study of the US Black Liberation Movement, this volume explores how agent provocateurs-and agent provoca­teur-like behavior-make movements smaller, weaker, and easier to de­feat. It also offers some ideas for how activists can inoculate their movements against such harms and increase their chances of success.