This volume is the second part of the book on "Chromatin Structure and Function", which resulted from a NATO-Advanced Study Institute held at Erice during April 1978. In addition to giving an updated and detailed description of various levels of chromatin organization, i. e. octamers, nucleosomes, multimers, solenoid and higher order fibers (including the most recent, yet unpublished, findings), it focuses, in a tutorial and organic format, on the possible mechanisms controlling transcription and on the basic biological phenomena (either genetic or epigenetic) related to cell aging, cell cycle, differentiation, transformation and chemical carcinogenesis. The most significant (sometime spirite~ discussion sessions have been included at the end of every section. Their clarifying nature is further supported by the final section (V), which summarizes and reviews the current state of the art on the genetic apparatus and its constituents. All chapters have selected up-to-date references; quite a few have an extensive bibliography both in terms of basic reference books and most recent findings. A few chapters, dealing at the level of intact cell and/or in classical genetic terms, with aging, differentiation and neoplastic transformation, have been included to furnish a more comprehensive view of fundamental cell functions directly and indirectly related to the structure and function of the genetic apparatus. At the same time it is hoped that interested students and investigators will find in the chapters of this volume the necessary and stimulating introduction to the wide variety of fundamental mechanism and phenomena occurring in higher eukaryotes.