Cardiac resynchronization therapy (CRT) is an established treatment for select patients with systolic heart failure, left ventricular conduction delay, and dyssynchronous contraction. Landmark trials have shown CRT’s benefits on symptoms, exercise capacity, reverse remodeling, hospitalization rates, and mortality. However, limitations exist including sub-optimal patient selection, procedural complexity, high non-responder rates, and device-related adverse effects. This review summarizes the evolution, physiology, clinical trial evidence, patient selection, delivery, and optimization of CRT. Key areas covered include guidelines for CRT use, invasive and noninvasive imaging to improve outcomes, alternative pacing sites to enhance response, and advances in lead technology and implantation techniques. Gaps in current knowledge are highlighted along with future directions for research to refine CRT utilization and improve real-world clinical outcomes. With further studies to address remaining questions, CRT is poised to become an even more effective therapy for heart failure patients with dyssynchronous cardiomyopathy.