The post-cold war era has seen an unmistakable trend toward the proliferation of violent non-state groups-variously labeled terrorists, rebels, paramilitaries, gangs, and criminals-near borders in unstable regions especially. In Borderland Battles, Annette Idler examines the micro-dynamics among violent non-state groups and finds striking patterns: borderland spaces consistently intensify the security impacts of how these groups compete for territorial control, cooperate in illicit cross-border activities, and replace the state in exerting governance functions. Drawing on extensive fieldwork with more than 600 interviews in and on the shared borderlands of Colombia, Ecuador, and Venezuela, where conflict is ripe and crime thriving, Idler reveals how dynamic interactions among violent non-state groups produce a complex security landscape with ramifications for order and governance, both locally and beyond. A deep examination of how violent non-state groups actually operate with and against one another on the ground, Borderland Battles will be essential reading for anyone involved in reducing organized crime and armed conflict-some of our era's most pressing and seemingly intractable problems.