Optimization of cardiac resynchronization therapy is increasingly performed. Numerous methods have been proposed, many being echocardiographic. Both the technique and the timing of optimization are contentious. Whether acute haemodynamic benefits translate into long-term improvements in remodelling, symptoms, or prognosis is unknown. Recent guidelines from the American Society of Echocardiography advocate routine optimization. Here, we objectively review the principles, methods, timing, and evidence supporting optimization. Despite limited validation, optimization was included in landmark clinical trials and is inherent in evidence-based practice. Randomized controlled trials comparing methods are needed, with long-term clinical endpoints. For now, optimization should be performed using the iterative method, according to the CARE-HF protocol.