They block the action of ACE an enzyme which converts Angiotensin 1 to Angiotensin 2.Usually used as hypertensives. Preferable drug in hypertensive patients with diabetes. All drugs end with -pril. Eg. Enalapril. Most of them are prodrugs. Except Captopril and lisinopril. Common side effect is dry cough, due to accumulation of bradykinin which is also metabolised by ACE