Some of the current concepts used in transgenic research, an increasingly important tool to study the regulation and function of genes, are illustrated in this book. With these techniques, animal models can be used to study human diseases; this opens up new possibilities in both applied and basic research. Specifically, the ability to introduce genes into the germline of mice and the successful expression of the inserted gene within an organism provide new insights and opportunities for biomedical research. The discussion here shows how a detailed analysis of the underlying molecular mechanisms will provide new insights into the genetic origin of certain diseases and will lead to a better understanding of normal and abnormal physiological processes.