The introduction explains the need for understanding unintended effects in international development. It starts with a problem statement that unintended effects, both positive and negative, are all too often overlooked in the international development sector. It then discusses five myths about unintended effects that need to be unlearned: (1) unintended effects can’t be anticipated, (2) unintended effects are unavoidable, (3) unintended effects are always downplayed, (4) unintended effects are always negative, and (5) unintended effects are an objective phenomenon. It lays out the target audience: policymakers, practitioners, evaluators, and students of development. It sets out the scope and ambitions of the book, and gives a reading guide for the book.