In wide and active continental plate boundary zones, ductile flow in the deeper and strong parts of the lithosphere may control crustal deformation. This is likely if average resistive shear stresses on faults in the brittle crust are much less than 108 Pa and the underlying bulk effective viscosity is much greater than 1021 Pa s. In this case, a simple model of distributed deformation, referred to as the floating block model, may be useful. This treats the crust as an array of rotating and translating rigid blocks, where are floating on an underlying continuous flow with a constant rheology. The model is analyzed in detail in this paper because it has the potential to link detailed observations of crustal deformation with the large-scale flow. Crustal blocks are defined by at least two sets of faults. The kinematics of crustal deformation can be described in terms of the motions of these blocks. Both the relative motion on block boundaries (faults) and block tilting about a horizontal axis can be described in terms of the underlying flow and block rotation about a vertical axis. However, rotations about a vertical axis, which are an important component of the crustal deformation, will depend not only on the underlying flow but also on the shape, orientation and arrangement of the crustal blocks. The average rotation rate about a vertical axis, over finite rotations, will be significantly different from that predicted at any instant. Also, the rotation history is considerably complicated if, as is likely, the underlying flow field, or block shape, has changed with time. These aspects of crustal deformation are discussed with reference to real zones of active deformation in New Zealand, Greece and western North America.