Psoriasis is a chronic inflammatory skin condition that is often associated with systemic manifestations. It affects about 2 percent of U.S. adults, and can significantly impact quality of life. The etiology includes genetic and environmental factors. Diagnosis is based on the typical erythematous, scaly skin lesions, often with additional manifestations in the nails and joints. Plaque psoriasis is the most common form. Atypical forms include guttate, pustular, erythrodermic, and inverse psoriasis. Psoriasis is associated with several comorbidities, including cardiovascular disease, lymphoma, and depression. Topical therapies such as corticosteroids, vitamin D analogs, and tazarotene are useful for treating mild to moderate psoriasis. More severe psoriasis may be treated with phototherapy, or may require systemic therapy. Biologic therapies, including tumor necrosis factor inhibitors, can be effective for severe psoriasis and psoriatic arthritis, but have significant adverse effect profiles and require regular monitoring. Management of psoriasis must be individualized and may involve combinations of different medications and phototherapy.