Diurnal period wind stress and current fluctuations measured over the continental shelf off northern California during the Coastal Ocean Dynamics Experiment in the summers of 1981 and 1982 are examined. The diurnal currents are strongly surface intensified, with amplitudes of up to 20 cm s-1. At depths of less than 35 m, the diurnal currents are nonstationary, and their amplitude is well correlated with the amplitude modulation of the local diurnal wind stress. Beneath the surface layer, the diurnal current vectors rotate clockwise with ellipse semi-major axes of 1 to 3 cm s-1. A mixed layer model driven with diurnal wind stress and surface heat flux produces currents similar to those observed in the upper water column. The deeper currents are consistent with the combination of a freely propagating Kelvin and first-mode coastal-trapped wave and, over the inner shelf, with the interior flow forced by the diurnal wind stress in the presence of a coast. ¿ American Geophysical Union 1988