Diuretics are drugs that decrease the volume of the extracellular fluid by increasing renal salt and water excretion. They can be divided into several groups regarding their chemical structure, operating mechanism and site of action: loop diuretics (furosemide, bumetanide, torasemide, ethacrynic acid), thiazide and thiazide-like diuretics (hydrochlorothiazide, chlortalidone, metolazone, indapamide), potassium- sparing diuretics (amiloride, triamterene), aldosterone receptor blockers (spironolactone, eplerenone), carboanhydrase inhibitors (acetazolamide), osmotic diuretics (mannitol), and vasopressin antagonists (tolvaptan, lixivaptan, conivaptan). Indications for diuretics administration are very broad: fluid retention (heart failure, cirrhosis, nephrotic syndrome), hyperkalaemia, arterial hypertension, nephrogenic diabetes insipidus, hypercalciuria, hyperaldosteronism. In the treatment of arterial hypertension diuretics represent one of the essential drugs either as monotherapy or in combination with other antihypertensives. In patients with heart failure they are given to all patients with clinical signs or symptoms of pulmonary or systemic venous congestion.