The renin-angiotensin system has been established as an attractive target for pharmacological intervention since the discovery of first angiotensin-converting enzyme inhibitors (ACE-Is). In fact, these drugs are primarily used in the management of cardiovascular system-related diseases and renal insufficiency. Their mechanism of action involves the adjustment of balance between vasoconstrictive, hypertrophic and salt/water-retentive angiotensin II and vasodilatory and natriuretic bradykinin by the inhibition of angiotensin II biosynthesis and bradykinin degradation. Currently there are thirteen family members approved for use in humans. They differ in structure, chemistry and pharmacokinetic and pharmacodynamic properties yet they display a similar pharmacologic and toxicologic profile. All of them are effective in the treatment of hypertension as well as in cardiac insufficiency or diabetic nephropathy. Although they are generally well-tolerated several serious side-effects including life-threatening angioedema, renal failure and persistent dry cough could occur during the administration of ACE-Is, which may require the cessation of therapy. Furthermore, to provide maximum safety and efficiency of ACE-Is-based therapy, the knowledge of the related drug interactions and chronokinetics seems to be an absolute requirement. Here we discuss the above-mentioned issues regarding the pharmaceutical and chemical properties of the commercially- used ACE-Is.