Book excerpt: United Nations peacekeeping constitutes the second largest military deployment around the world, and the organization's flagship enterprise. Once responsible simply for the job of observing frontiers and monitoring ceasefire agreements, UN missions are now frequently charged with the far more daunting task of 'robust' intervention- penalizing spoilers of peace and protecting civilians from peril. Taking Sides in Peacekeeping explores this transformationand its implications through the first comprehensive conceptual and empirical study of impartiality, a norm long considered to be the bedrock of UN peacekeeping. It reveals how a change in the dominantunderstanding of impartiality has politicized peacekeeping and, in some cases, effectively converted UN forces into one warring party among many. The book incorporates a large body of primary evidence and draws on extensive fieldwork in the Democratic Republic of the Congo, site of the biggest and costliest mission in UN history (1999-2015).