Diseases of the nail unit may have numerous causes that reflect dermatology as a whole but often present in a unique way. This chapter attempts to increase insight into the pathophysiology of the expression of nail abnormalities. It also focuses on many groups of nail disease, including traumatic nail disorders, tumours of and around the nail unit, perionychial disorders, age‐related nail abnormalities, and frequent dermatoses affecting the nails, such as nail psoriasis, eczema and lichen planus. Imaging of the nail, nail surgery and some cosmetic aspects of nail care are also discussed.