Lupus erythematosus (LE) is an inflammatory connective tissue disease of generalized autoimmunity characterized by pathogenic autoantibodies and immune complexes, attributed to loss of immune tolerance. Cutaneous involvement, which appears in the majority of patients with the disease, can present as LE-specific or LE-nonspecific manifestations. The LE-nonspecific manifestations include e.g. vascular skin changes and may be associated with systemic organ manifestations or other autoimmune diseases. In contrast, the LE-specific manifestations encompass the various subtypes of cutaneous lupus erythematosus (CLE), which are classified as separate entities without or with less severe systemic organ involvement. In the “Duesseldorf Classification”, CLE is subdivided into four different categories: acute CLE (ACLE), subacute CLE (SCLE), chronic CLE (CCLE), and intermittent CLE (ICLE). Differentiation between these subtypes is based on clinical features and average duration of the cutaneous lesions, but can also consider histological changes of skin biopsy specimens and laboratory abnormalities. In addition, direct immunofluorescence and photoprovocation may be applied to confirm the diagnosis in specific cases. Further investigations should be considered dependent on the clinical symptoms of the CLE patient and the results of the laboratory tests. A revised scoring system, the Cutaneous Lupus Erythematosus Disease Area and Severity Index (RCLASI) has recently been validated to assess disease activity and damage in CLE. In this review, we focus on the classification of CLE and the diagnostic procedures to identify and confirm the different subtypes of the disease.