Series of observations of the sea breeze has been made along a portion of the New England coast near Block Island, Rhode Island. These observations were presented in an earlier paper (Fisher, 1960). With these data as a basis, a dynamical theory of the sea breeze is described and a numerical solution of these sea-breeze equations is obtained. The solution shows the sea breeze in the stages of development and decay and succeeds in reproducing not only the gross features of the wind system but many of its small details as well. The model sea breeze develops a cellular structure similar to the observed system. The depth of the landward branch of the current, its velocity, the velocity of the return current aloft, the elevation, location, and timing of the maximum flow, agree closely with observations. The model also reproduces the rotational effects due to the Coriolis force. The accumulation of error in the model causes its behavior to become irregular by evening (14 hr from its start) so that the development of the low-level jet and other features of the dying system can only be poorly evaluated in the model.