Skin neoplasms are one of the most common diagnoses among patient encounters. Evaluating both benign and malignant neoplasms is vital, particularly due to the increasing incidence of skin cancers and complications associated with the condition. Skin cancer has multiple etiologic factors, with UV radiation-induced DNA damage and oncogenesis being the most prominent. Preventive strategies, such as sunscreen application, are essential in reducing risk. After evaluation by a trained healthcare provider, a biopsy is typically performed, and histopathological evaluation helps confirm the diagnosis and differentiate the type of skin cancer from other conditions. Management of skin cancer may involve observation, topical therapies, local non-topical treatments (eg, antineoplastic medication injections), systemic regimens (eg, chemotherapy and immunotherapy), radiation therapy, and surgical or procedural interventions (eg, Mohs micrographic surgery and cryosurgery). The skin's anatomical complexity allows skin cancer to arise from any of its cells or components. The proliferation of cells in skin cancer can be benign or malignant (see  Anatomy of the Human Skin). Please see StatPearls' companion resource, "Anatomy, Skin (Integument)," for more information on skin anatomy. In standard literature, malignant skin cancer is typically categorized into melanoma and nonmelanoma skin cancers, which usually refer to basal cell carcinoma or squamous cell carcinoma. However, this classification can be problematic, as skin cancer can originate from various cells and subdivisions of the skin. Benign epidermal tumors may include epidermal nevi, pseudoepitheliomatous hyperplasia (eg, prurigo nodularis), and acanthomas (eg, seborrheic keratosis). Premalignant dysplasia, such as actinic keratosis and arsenical keratosis, may also be present. Malignant tumors of the epidermis include intraepidermal carcinoma (eg, Bowen disease), basal cell carcinoma, squamous cell carcinoma, and verrucous carcinoma. Please see StatPearls' companion resources, "Seborrheic Keratosis," "Clear Cell Acanthoma," "Cutaneous Horn," "Keratoacanthoma," "Cutaneous Melanoacanthoma," "Cutaneous Squamous Cell Carcinoma," "Intraepidermal Carcinoma," and "Basal Cell Carcinoma," for more information on common epidermal tumors. Pigmentary lesions include those with basal melanocytic proliferation (eg, solar lentigo), junctional or dermal melanocytic lesions (eg, Spitz nevus), dysplastic lesions (eg, dysplastic nevus), and malignant lesions (eg, melanoma, clear cell sarcoma). Please see StatPearls' companion resources, "Subungual Melanoma," "Lentigo Maligna Melanoma," "Metastatic Melanoma," "Dysplastic Nevi," "Atypical Mole," "Acral Lentiginous Melanoma," and "Congenital Melanocytic Nevi," for more information on pigmentary lesions relevant to skin cancer.  Skin cancer may arise from cutaneous appendages, such as hair follicles (eg, desmoplastic trichoepithelioma), sebaceous glands (eg, sebaceous adenoma and sebaceous carcinoma), apocrine glands (eg, spiradenoma), and eccrine glands (eg, porocarcinoma). Please see StatPearls' companion resources, "Desmoplastic Trichoepithelioma," "Sebaceous Carcinoma," "Syringoma," "Spiradenoma," "Trichoblastoma and Trichoepithelioma," and "Cylindroma," for more information on tumors of cutaneous appendages. Fibrous tissues of the skin can also proliferate, leading to skin cancer, such as dermatofibroma and its malignant counterpart, dermatofibrosarcoma protuberans. Please see StatPearls' companion resources, "Dermatofibrosarcoma Protuberans" and "Dermatofibroma," for more information on fibrous tumors.  The presence of fat, muscle, cartilage, and bone can lead to skin cancers such as liposarcoma, leiomyosarcoma, chondroma, and osteosarcoma (although osteosarcoma may be considered metastatic by some). Please see StatPearls' companion resources, "Atypical Fibroxanthoma" and "Leiomyosarcoma," for more information on fat, muscle, cartilage, and bone tumors.  Benign and malignant skin cancers can arise from neural tissue, such as Merkel cell carcinoma and schwannoma, or from vascular tissue, such as hemangioma and angiosarcoma. Please see StatPearls' companion resources, "Angiolymphoid Hyperplasia With Eosinophilia," "Angiosarcoma," "Merkel Cell Carcinoma of the Skin," "Neurothekeoma," "Hemangioma," "Cutaneous Vascular Malignancies," "Angiosarcoma," " Kaposi Sarcoma," and "Cutaneous Angiofibroma," for more information on common tumors of neural and vascular origin. Infiltrative skin cancers can arise from various immune cells that reside in the skin, including mastocytoma, xanthoma, Langerhans cell histiocytosis, T-cell lymphoma, natural killer (NK)—cell lymphoma, and B-cell lymphoma. Please see StatPearls' companion resources "Sezary Syndrome," "Extranodal NK-Cell Lymphoma," "Peripheral T-Cell Lymphoma," "Dermatopathology Evaluation of Cysts," "Mastocytoma," "Mycosis Fungoides," and "Lymphomatoid Papulosis," for more information.