This is the first book to cover and explore the rules and exceptions in biology. It presents past and current perspectives on the subject and discusses the various situations of transition from rule to exception and vice versa. In doing so, the book fills a gap in the scientific literature and stimulates useful and valuable discussions among researchers working in biology worldwide. The chapters begin with a theoretical framework, followed by the main topic(s) or question(s), and a summary of previous work on the topic. Examples are discussed, with concluding remarks and suggestions for future research. A section with key concepts is included at the end of each chapter, allowing the reader to jump directly to the most important findings or observations. Each chapter is written to be used as a reference by graduate students and professionals from a variety of scientific disciplines (e.g. behavior, ecology, evolution, and systematics).