An internationally accepted classification system of chronic venous disease (CVD) is mandatory to understand the natural history and epidemiology of the disease and to compare results of treatment and prophylaxis. The CEAP classification is the international gold standard in CVD classification. The first CEAP classification was published by the American Venous Forum (AVF) in 1996. It is based on clinical manifestations (C), etiologic factors (E), anatomic distribution (A), and the underlying pathophysiology (P). A first revision with clear definitions was published in 2004. In 2020, the second revision with substantial improvements was published. In the clinical part (C), recurrent varicose veins are added as C2r and corona phlebectatica paraplantaris as C4c, as well as recurrent active venous ulcer as C6r. In the etiological part (E), the secondary etiology is divided into secondary intravenous (Esi) and secondary extravenous (Ese) etiology. CEAP is not a severity classification, although it is used as this in several papers. For the severity classification of CVD, other instruments like the revised venous clinical severity score (rVCSS) should be used.