This chapter provides an in-depth update on the pharmacology, clinical use, side effects, and follow-up of retinoid therapy in dermatology, this source and addresses topics related to retinoid use in special circumstances, including vulnerable populations, concomitant surgery, and aesthetic procedures. The importance of vitamin A has been recognized for over 3500 years, especially as a factor in treating deficiency diseases. By the late nineteenth century, the effects of vitamin A deficiency on growth had been recognized, and milk was discovered to be essential for healthy growth in the laboratory. By 1971, the use of retinoid therapy had been expanded with the introduction of oral tretinoin for the treatment of hyperkeratinization disorders, psoriasis, and even skin tumors. Retinoids, both topically and systemically, continue to be a significant part of the dermatologic armamentarium, in particular for the treatment of acne, psoriasis, cutaneous T-cell lymphoma, and keratinization disorders.