Plants possess the ability to biosynthesize a large variety of steroids, but it was not until 1979 that a hormonal function was demonstrated in plants. Today, about 40 structurally and functionally related steroids, known as brassinosteroids, have been isolated from natural sources. Brassinosteroids demonstrate various kinds of regulatory activities in the growth and development of plants. This book is based on a 1990 Russian monograph, but includes all important subsequent literature and developments, including unpublished data from the authors' laboratories.