The nail unit is a complex skin appendage situated on the dorsal surfaces of the fingertips and toes. It serves crucial roles in both protection and sensory perception, enhancing our daily functional abilities. This structure consists of several integral components: the nail plate, nail bed, nail matrix, and periungual folds. The nail plate, the visible part of the nail, is produced through ongoing cellular differentiation within the nail matrix and is firmly anchored to the nail bed by the surrounding folds, extending distally to form its free edge. A thorough understanding of the anatomy and terminology associated with the nail unit is essential for accurately recognizing and interpreting various conditions and changes affecting this area. This chapter offers a detailed overview of the nail unit anatomy, describing each of its constituent structures. It lays the foundation for visualizing these structures through imaging techniques, with a focus on ultrasonography and magnetic resonance imaging with surface coil.