Vitamin D is a fat-soluble vitamin that is naturally found in very few food sources. It is produced endogenously from ultraviolet light from the sun striking the skin and then triggering vitamin D synthesis and activation. Vitamin D helps promote calcium absorption in the gut, maintains adequate serum calcium and phosphate levels, promotes bone growth, modulates cell growth, and has many other roles. There have been an increasing number of people, especially in older adults, with vitamin D deficiency. This is in part a result of a reduction of sun exposure as people age, increase in use of sunscreen, and other factors. This article highlights the roles of cholecalciferol (vitamin D3) versus ergocalciferol (vitamin D2) supplementation for practicing pharmacists.