Cutaneous drug reactions are the most frequently occurring adverse reactions to drugs. Among hospitalized patients, the incidence of these reactions ranges from 1 to 3%. The frequency of cutaneous reactions to specific drugs may exceed 10%. These reactions may range from mildly discomforting to those that are life-threatening. Anti-infective and anticonvulsant agents are among the drugs most commonly associated with adverse reactions in the skin. We describe and illustrate the clinical morphology of the most common cutaneous drug reactions, as well as drugs that most commonly precipitate specific reactions. The varied nature of the reactions that do occur, even with specific agents, indicates a multiplicity of mechanisms available whereby cutaneous drug reactions may be initiated. Although a variety of terms have been proposed for categorizing cutaneous drug reactions, we propose that reactions are best defined based upon mechanisms, where known. In this review, we assess the current knowledge of four categories of cutaneous drug reactions: immediate-type immune-mediated reactions, delayed-type immune-mediated reactions, photosensitivity reactions, and autoimmune syndromes. Moreover, we describe evidence that viral infection is an important predisposing factor for the development of cutaneous drug reactions upon drug administration. Finally, we review the current knowledge of the type and mechanisms of cutaneous drug reactions to several categories of drugs.