In the paper, the currently available studies are presented, which deal with the vitamin B₁₂ (cobalamin), its structure, the biochemical pathways of its biosynthesis, its importance for human health, as well as with the methods of determining it. In addition, research results into the biotechnological production of vitamin B₁₂ are reported. The vitamin B₁₂ is an important co-factor for the metabolism of carbohydrates, lipids, amino acid, and nucleic acids in the human body. It is also an anti- pernicious anaemia factor. The cobalamin biosynthesis is almost exclusively restricted to the prokaryotic organisms. Many bacterial species are able to synthesize vitamin B₁₂, but only appear significantly important: Propionibacterium freudenreichii and Pseudomonas denitrificans.