This chapter provides detail description of vitamin B complex. Chapter has 18 well-illustrated diagrams and pictures. Biochemistry and metabolism of vitamin K, sources, requirement, functions of vitamin B complex, Physiological role of vitamin B complex, deficiency signs of vitamin B complex, dietary sources, stages of beriberi, riboflavin, niacin, clinical settings of pellagra, pyridoxine, biogenic amines with functions, folic acid, folic acid in pregnancy, neural tube defects, biotin, vitamin B12, megaloblastosis, pantothenic acid and coenzyme A are given in detail. 19 tables are included to highlight deficiency signs of B complex, dietary source of B complex, recommended intake of thiamine, niacin, riboflavin, pyridoxine, folic acid, biotin, B12 pantothenic acid. 66 references are given at the end of the chapter for further reading.