It is now about 100 years since the chloroplast has been recognized as the site of photosynthesis in plant cells. The last 20 years have seen a striking increase in interest in the structure and function of the chloroplast. Hastened on by powerful new tools such as the electron microscope and the newer methods of isolation and analysis of chloroplasts, there is presently considerable experimental work on the properties of this organelle. In such a rapidly moving field and one which is reviewed systematically is various Annual Reviews, it is not possible to present a detailed critique of the prolific literature in a book of reasonable size. Rather the decision was made to sacrifice complete coverage of the field and to indicate general areas of investigation. In organization, problems here dealt with, are those concerned with the electron microscopy of chloroplast structure, development and conformation, genetic control of chloroplast development, characterization of some of the major components of the chloroplast and the biochemical properties of the chloroplast including the for mation of adenosine triphosphate and reduced pyridine nucleotide and the assim ilation of carbon dioxide into carbohydrate with subsequent conversion to second ary products. A historical outline on the general subject "Photosynthesis and the Chloroplast" has been included to place into proper perspective the rapid developments in the several areas covered in the book. I am particularly indebted to Dr. Roy E.