The quality and detail of an image obtained by gamma cameras are affected by several parameters associated with these imaging systems. These parameters include spatial resolution, sensitivity, uniformity, and contrast, and they are described here in detail. The details of how these parameters affect image formation and the remedies thereof are elaborated. A discussion on the characteristics of different collimators and their effects on image formation is presented. A brief description of the daily, weekly, and annual quality control tests for gamma cameras is also included.