In this paper, a digital Particle Image Velocimetry (PIV) technique is described. The advantages of the technique in measuring velocity fields is illustrated by its applications to the measurement of the wake flow behind a circular cylinder. Single frame and multiply exposed digital particle images were acquired using a CCD camera. The velocity calculation is based on the digital Young's fringe pattern. Digital image enhancement techniques have been used to improve the quality of image signals. A data validation method which can detect and reject false data points effectively has been developed. The near-wake instantaneous velocity distributions, with approximately 2000 points per frame, were collected for a Reynolds number ranging from 125 to 660 based on the cylinder diameter. Vorticity and circulations of shed vortices are presented. The plane normal to the classic vortex street was also measured; on this plane the footprint of embedded counter-rotating longitudinal vortex pairs are clearly evident.