This short book is distinguished by : 1) its systematic and comprehensive approach to the under-explored subject of unintended consequences; 2) its focus on the inherent unpredictability of human action as a major cause of such consequences; 3) its contention that these consequences pose serious challenges to the way in which moral philosophy has been done in the past; and 4) its exploration of methods and structures to help us identify possible unintended consequences before we act and to enable us to better cope with them as they arise.