The skin is host to one of the most diverse arrays of developmental anomalies, hamartomas, and benign and malignant neoplasms encountered in any organ system of the body. Epithelial, mesenchymal, hematopoietic, and melanocytic proliferations are commonly encountered in the skin and comprise a large part of most routine pathology practices. This chapter describes the clinical and histopathologic features of these proliferations, in addition to describing the special studies such as immunohistochemistry often necessary to arrive at the correct diagnosis. As in all areas of surgical pathology, but especially in dermatopathology, the correct diagnosis requires correlation of the microscopic findings with clinical information. This chapter will also cover immunodermatology and specifically the application of direct and indirect immunofluorescence to the diagnosis of immune-mediated bullous disorders and other autoimmune dermatoses.