Contemporary views on the structure and function of chromatin are presented and the history of the development of these ideas as well as the nature of the nucleic acid and protein components of chromatin are reviewed. The structure of chromatin is studied at several levels, and its modes of transcription and replication are analyzed. Chromatin provides researchers with a critical evaluation of current knowledge. It combines much information that has never before been assembled, and evaluates and interrelates it in a critical way. This has not been done before so that readers are not only provided with an overview, but with extensive references to the literature (there are about 2000 references in all).