Cardiac resynchronization therapy (CRT) is an established treatment for patients with advanced heart failure, cardiomyopathy, and interventricular conduction delay or wide QRS complex. Use of this treatment is supported by a multitude of clinical trials that have demonstrated its benefits on clinical parameters such as exercise capacity, heart failure functional class, and quality of life. More recently, CRT has been shown to reduce total mortality rates in patients with heart failure. Many questions have yet to be answered, however, including how to better identify patients for this therapy and how to potentially expand its clinical indications to other groups of patients. This article reviews the published literature supporting the current indications and addresses some of the issues that may change how this therapy is utilized in the future.