The operation and performance of an array photometer with the ability to discriminate on single photoelectrons will be discussed. The University of Maryland Array Photometer is a system which consists of a 100 by 100 array of channels which count single photoelectrons. The photosensor is an Intensified Charge Coupled Device using a Fairchild CCD201 which was fabricated by the Electronic Vision Company. This system has demonstrated a noise level which permits single photoelectron discrimination, high scan rate (400 frames/ sec), and low lag. The system and its performance will be discussed. The UMAP system has been successfully operated in the photon counting mode on a 36-inch telescope and on a 48-inch telescope. Data from these observations will be discussed, to illustrate the system sensitivity and the spacial resolution which is better defined by the size of an individual pixel element on the CCD.