Coenzymes are small complex organic molecules that mostly originate from vitamins and other essential nutrients. They are common in nature and they participate in enzymatically catalysed reactions. Vitamin B coenzymes are some of the most important coenzymes in the human metabolism and they are responsible for various functions that enable normal functioning of the cells in everyday life. Their function plays a part in the improvement of metabolism, the immune system, and the nervous system, as well as preserving the skin and the muscles, aiding in the growth and division of cells, and many other positive effects for the health of the organism. A deficiency of one or more of those coenzymes has a negative effect on the metabolism, and ultimately on the human health. Coenzymes from the vitamin B complex are: thiamine-pyrophosphate ( TPP ), flavin-mononucleotide (FMN), flavin-adenine-dinucleotide (FAD), nicotinamide-adenine-dinucleotide (NAD+ ), nicotinamide-adenine-dinucleotide-phosphate (NADP+), coenzyme A ( CoA ), pyridoxal-5’-phosphate (PLP), biocytin, tetrahydrofolate (THF), and coenzyme \( B_{12} \). The common evolutional origin of these coenzymes has made them essential for in vivo cellular metabolic processes. The aim of this paper is to describe the coenzymes of the vitamin B complex and their functions in biosynthesis. Coenzymes like nicotinamide and flavin oxides in oxidoreductases are the first considered coenzymes in nature, while variants of those organic molecules have been discovered only recently.