This monograph is intended to provide an overview of the structure, function, and development of the chloroplast. It should be viewed as a beginning of the study of chloroplasts and not as an end. In keeping with an introductory approach, abbreviations generally have not been used, so that substance is not replaced by symbol. The principal aim has been to provide a teaching tool to introduce students to the major characteristics of the chloroplast, with as much emphasis on mech- anisms as possible at this level. It was written for students with an advanced college level education in biology and chemistry who also have some knowl- edge of biochemistry. The fundamentals of these subj ects cannot be included in a book of this type. However, to provide a meaningful description of how the chloroplast works, Le. , what the mechanisms of photosynthetic reactions are, the subj ect must be dealt with at the molecular level. Living systems are chemical systems, and the importance of understanding these systems at the molecular level cannot be overstated. Therefore, although attempts were made to keep the chemistry at a relatively simple level, occasionally statements are made that can be understood only with a sufficient background knowledge of chemistry. It is important for students to realize in broad outline form the functions of the chloroplast and where its functions fit into the scheme of life.