Publisher Summary This chapter summarizes the results obtained in capping/cytoskeleton research. There are two types of capping phenomena: ligand-dependent and ligand-independent processes. A number of different reagents, such as colchicine and hypertonic media, can cause the formation of cap structures in the absence of any externally added ligand. Morphological studies, using both transmission and scanning electron microscopy, of cells forming caps in hypertonic medium have identified a strong association between cap structures and microvilli. External ligand (antibody, lectin, or some hormones) mediated receptor patching and capping is responsible for important immune-related responses: ( 1) proliferation and differentiation of the cells into antibody-secreting plasma cells, (2) the development of an increased number of precursor cells which are responsible for immunological memory, and (3) the activation and proliferation of T cells which carry out cell-mediated cytotoxic killing. In nonimmune cells, capping may also be involved in important cellular processes, such as endocytosis, chemotaxis, mitogenesis, and general cell–cell recognition.