This book is a collective monograph prepared by scientists from Russian Peoples’ Friendship University. The purpose of this book is to show the importance of the codification’s process for development of international environmental law (IEL) and to describe different forms of IEL’s legal sources This monograph has a good structure and consists of 5 chapters. In the first chapter authors analyze key concepts of IEL, such as “codification of International Environmental Law” and “soft law”. The second chapter is dedicated to description of principles of IEL. The roles of international governmental organizations (UN, FAO, IMO, ICAO and IAEA) and nongovernmental organizations (IUCN, WWF, Greenpeace International, ICRC) in process of codification and progressive development of IEL are discussed in Chapter III and Chapter IV of this monograph. In the last Chapter authors describe problems of IEL’s codification during the UN environmental conferences (Stockholm 1972, Rio 1992 and Johannesburg 2002).In conclusion, we can say that this book is important and may contribute to the development of Russian’s IEL doctrine.