Most nonmelanoma skin cancers (NMSCs) are basal cell carcinomas (BCCs) or squamous cell carcinomas (SCCs). However, several rarer forms of NMSC exist, including four malignant neoplasms discussed in this chapter: sebaceous gland carcinoma, Merkel cell carcinoma, angiosarcoma, and dermatofibrosarcoma protuberans (DFSP). Each of these neoplasms is discussed separately after a summary of genetic alterations in BCC, SCC, and selected genodermatoses. Understanding the genetic basis of skin cancer is an important step in improving prognosis among patients with these neoplasms. Analysis of germline mutations in familial cancer syndromes and somatic mutations in sporadic skin cancers is providing new information that will facilitate the diagnosis of cutaneous malignant diseases and revolutionize their management.