The term "Chronic critical ischemia ", CCI, of lower limb defines a very advanced state of chronic LL arterial insufficiency with deleterious effect of low perfusion pressure rate. This diagnosis has serious consequences for the patient (high risk of major amputation, high risk of cardiovascular events and death, high risk of reduced quality of life for survivals even non-amputated). The diagnosis must be precise. We discuss the evolution of the concept and the definitions of CCI from Fontaine classification, the epidemiology of CCI and its risk factors, the diagnosis of CCI (clinical, haemodynamical, anatomical) and the treatment of CCI which the main goal is to increase as much as possible the arterial pressure in the foot.