Publisher Summary This chapter describes the stabilization of chloroplasts and subchloroplast particles. The technology of the stabilization of soluble enzymes, through chemical manipulations designed to protect them from deactivation, has made exceedingly rapid progress recently. In contrast, comparatively little has been achieved with membrane-integrated systems, such as those in the photosynthetic membranes of green plants, in spite of their undisputed technological future as solar energy converters. This chapter describes the attempts to stabilize the structure-dependent functions of only the isolated higher plant chloroplasts. Although the very first step of such endeavors is to prepare active chloroplasts, conditions necessary for that are reviewed briefly. Emphasis is placed on chemical manipulations of chloroplast membranes, and in particular on protein covalent cross-linking techniques, and the effects these have on the functions and the functional life of isolated chloroplasts. Factors contributing to the inactivation of isolated chloroplasts are elaborated. Factors whose presence in the isolation and storage media improves the activities of chloroplasts preparations are presented in a table. Cross-linking of chloroplast membrane proteins with bifunctional reagents is described. The properties of isolated spinach chloroplasts after reaction with glutaraldehyde and dimethyl suberimidate are also discussed in the chapter.