Vitamin B12 is unusual with respect to its origins. While most vitamins can be made by a wide variety of plants and specific animals, no plant or animal has been shown capable of producing B12, and the exclusive source of this vitamin appears to be tiny microorganisms like bacteria, yeasts, molds, and algae.

Like most vitamins, B12 can occur in a variety of forms and can take on a variety of names. Names for B12 include: cobrynamide, cobinamide, cobamide, cobalamin, hydroxcobalamin, aquocobalamin, nitrotocobalamin, and cyanocobalamin. Each of these designations contains a form of the word "cobalt," since cobalt is the mineral found in the center of the vitamin.