Dermoscopy is a noninvasive, in vivo method for the early diagnosis of malignant melanoma and the differential diagnosis of pigmented lesions of the skin. By allowing visualization of sub-macroscopic pigmented structures that correlate with specific underlying histopathologic structures, dermoscopy provides a more powerful tool than the naked-eye examination for clinicians to determine the need to excise a lesion. This article reviews the principles of dermoscopy, the most common dermoscopic patterns associated with nevi and melanoma, and the factors influencing the nevus pattern in a given individual.