The use of null models - statistical models and computer simulations used to analyze patterns in nature, and used in ecology since the 1970s - is a controversial one: detractors argue that premises built into them often determine conclusions, while advocates see them as basic tools. This book provides the first overview of this complex and controversial subject, taking up significant areas of research that have been subjected to null model analysis, including niche overlap, community assembly, the species-area relationship, and food web structure.