Polycaprolactone (PCL) is a thermoplastic biodegradable polyester, which has had biomedical application in the 1970s and 1980s as a long-term drug delivery systems, which then gained acceptance from the Food and Drugs Administration. However, due to very slow degradation, PCL was replaced by faster degrading polymers, such as polyglycolide, polylactides and their copolymers. The polymer gained popularity again in the 1990s, together with the development of tissue engineering. This book discusses the properties, applications and examines new research of polycaprolactones.