This chapter describes the chloroplast membrane polypeptides. Spectacular progress has been made in the field of separation and identification of chloroplast membrane polypeptides over the last decade, because of the development of SDS (sodium dodecyl sulfate)-polyacrylamide gel electrophoresis techniques and their application to the separation of chloroplast membrane polypeptides derived from a variety of sources. This method provides a rapid and accurate means for the analysis of purity of membrane fractions or isolated active complexes, of changes in membrane composition during development, or as a result of mutations, identification of subcellular origin of membrane polypeptides. In addition, large-scale gel electrophoresis has enabled the isolation of specific polypeptides for analysis of their amino acid composition or to serve as antigens. The wide application of this technique has inevitably resulted in a large number of modifications of the basic method to suit the material obtained from different sources. This chapter describes the general methodology that can be applied to the separation and identification of different membrane polypeptides as well as the possible use of this technique, in combination with other techniques, for the study of chloroplast membranes.