The ecology of populations is the study of the patterns of distribution and abundance of organisms. It also goes beyond mere description and seeks the evolutionary forces that might produce such patterns, and their ecological constraints. This book is on the ecology of populations but it is not a population ecology textbook. Therefore, there will be much standard textbook material left out. This book does not attempt to establish a new field, or summarize or synthesize an old one. Neither does it provide the student of population biology with all the necessary tools for further exploration, nor does it review the entire discipline, or parts of it. So what does this book do? As with most books, it presents an idiosyncratic world-view. We hope that some well-known problems and phenomena are getting a fresh and novel approach. We also hope that applying basically the same analytical tool to a number of seemingly disparate problems in population biology will be convincing enough to make others do likewise. By using rather simple models of population change to a large number of problems, we hope that conceptual unification will be promoted. Science becomes more and more specialized with the risk of losing track of the bigger picture. Although no bigger picture is presented here in a coherent way, the approach we have taken to address problems in population ecology aims at getting to that more synthetic understanding.