Vitamin supplements and therapies have recently gained popularity because of current scientific studies supporting their benefits. Although many consumers are taking vitamins and other supplements, they may not be aware of the numerous benefits and hazards associated with many of these over-the-counter substances. Clinicians should be familiar with common vitamin products so that they may prescribe and monitor their use. This article provides an overview of fat- and water-soluble vitamins, and addresses functions, deficiency effects, recommended dietary allowances, therapy uses, toxicity concerns, and food sources.