Skin biopsy provides tissue for histopathological diagnosis of dermatologic conditions. The choice of biopsy technique depends on the suspected diagnosis and lesion characteristics. The epidermis (0.05-1.5 mm thick) contains keratinocytes, melanocytes, and Langerhans cells. The dermis (1-4 mm thick) contains collagen, elastin, blood vessels, nerves, and adnexal structures. A shave biopsy samples the epidermis and superficial dermis, appropriate for superficial lesions where depth of invasion is not critical. A punch biopsy (2-8 mm circular blade) obtains a full-thickness cylinder through epidermis, dermis, and into subcutaneous fat, ideal for inflammatory dermatoses, vesiculobullous diseases, and panniculitis. Excisional biopsy removes the entire lesion with margins, used when melanoma is suspected (preserving Breslow depth) or for complete removal of a concerning lesion.