Systemic and pulmonary congestion is a central aspect of both acute and chronic heart failure and directly leads to many of the clinical manifestations of these syndromes. Therefore, diuretic therapy to treat congestion plays a fundamental role in heart failure management. However, although diuretics are the most common drugs prescribed for heart failure, there is limited quality evidence to guide their use. Unlike other components of the heart failure armamentarium, such as beta-blockers and angiotensin-converting enzyme inhibitors, diuretics (with the exception of aldosterone antagonists) have not been shown to decrease heart failure progression or improve mortality. Additionally, some observational data suggest that diuretics may actually be harmful in heart failure, contributing to neurohormonal activation, renal dysfunction, and potentially mortality. Despite these concerns, diuretics remain ubiquitous in heart failure management because of the need to address symptoms of congestion and the lack of alternative strategies. Recently, the development of a variety of potential adjuncts or alternatives to diuretic therapy has suggested the need for an active reappraisal of diuretic therapy for heart failure. The main classes of diuretics are the loop diuretics, potassium-sparing diuretics, and thiazides. Loop diuretics, the mainstay of acute and chronic therapy for heart failure, are "threshold drugs"; therefore, an adequate dose to achieve a pharmacodynamic effect (ie, to increase urine output) must be prescribed for effective therapy. The minimum dose to achieve diuresis and manage congestion should be used to minimize adverse effects. For patients refractory to initial dosing of intravenous diuretics, options include dose escalation, use of continuous infusion rather than intermittent boluses, or combination therapy with the addition of a thiazide or thiazide-like diuretic (eg, metolazone). Management of chronic heart failure often includes patient-directed titration of diuretics based on changes in symptoms or body weight in an attempt to decrease hospitalizations, although the efficacy of this strategy has not been tested in well-designed trials. Aldosterone antagonists, which are used primarily as neurohormonal agents rather than for their diuretic effects, are indicated for patients with systolic failure and moderate to severe symptoms, as long as renal function and serum potassium are stable and monitored closely. All diuretic therapy requires careful monitoring of electrolytes and renal function. Whether newer modalities for managing congestion (vasopressin antagonists, adenosine A(1) antagonists, and ultrafiltration therapy) will be an improvement over diuretic therapy will be determined by the results of multiple ongoing clinical trials.