In 1970 I wrote a review article for "Topics in Current Chemistry", surveying the general reaction patterns of transition-metal complexes from the standpoint of organic synthesis. The article seems to have evoked wide interest, and I therefore thought it appropriate to treat the subject more comprehensively in the form of a monograph. Organometallic chemistry is a rapidly growing field of intensive research. In this field, the application of organometallic compounds to organic synthesis is an important subject and many unique synthetic methods have been discovered, especially in the last decade. Syntheses using transition-metal com­ pounds are now in the foreground of organic chemistry. The purpose of this monograph is to give a bird's-eye view of this field to both organic and inorganic chemists through a mechanistic approach. A systematic unification of the voluminous data accumulated in this field is now urgently required. This subject is discussed by classifying various reactions into general patterns and by illustrating them with a limited number of pertinent examples.