This book attempts to trace the long history of some of the major ideas in the field and gives an account of our current knowledge of animal cytokinesis. It contains descriptions of division in different kinds of cells, as well as the proposed explanations of the mechanisms underlying the visible events. Experiments devised to test cell division theories are described and explained. The forces necessary to deform animal cells to the degree shown in cytokinesis now appear to originate from the interaction of linear polymers and motor molecules that have roles in force production and in the motion and the shape change that occur in other phases of the biology of the cell. The localization of the force-producing division mechanism to a restricted linear part of the subsurface is caused by the mitotic apparatus, the same cytoskeletal structure that ensures orderly mitosis.