Patellar instability is a generic term that is used to describe patellar dislocation, patellar subluxation, and general symptomatic instability. Patellofemoral instability is a relatively difficult condition to treat; accurate management of the condition should take into account the anatomy of the joint and its stabilizing structures. The goal of any treatment should be to restore the normal anatomy of the joint. It is important to understand the basic anatomy and biomechanics of this condition, the classification of different types of patellar instability, varying presentations, and diagnostic techniques and criteria, including the types of imaging studies that can be useful in determining the ultimate course of treatment.