This book was written at the invitation of Dr. H. GOTZE of Springer-Verlag for the series "Monographs in Endocrinology". It is not a comprehensive account of the prostaglandins but has been writ- ten with a deliberate emphasis upon those aspects of the field in which I am particularly interested and to which, in some cases, I have made a contribution. I am grateful to Miss E. PFISTERER and her colleagues of Springer- Verlag for their excellent work. I should also like to thank my wife without whose patience, encouragement and help this book would never have been completed. Finally this is an appropriate time to express my sincere gratitude to those scientists who over the years have given me samples of prostaglandins-namely Professors S.BERGSTROM and B.SAMUELSSON of the Karolinska Institute, Stockholm, Professor D. A. VAN DORP of the Unilever Research Laboratories, Vlaardingen and Dr. J. E. PIlm of the Upjohn Company, Kalamazoo. Without their help work in this field would have been extremely difficult.