This chapter provides detail description of Vitamin K. Chapter has 7 well-illustrated diagrams and pictures. Biochemistry and metabolism of vitamin K, sources, requirement, functions of vitamin K, epidemiology, vitamin E deficiency, Vitamin K epoxide cycle, vitamin K dependent protein in blood clotting, role in bone metabolism are given in detail. 4 tables are included to highlight forms of Menaquinones synthesized by intestinal bacteria, recommended nutrient intake by different age groups as per WHO, functions of vitamin K and vitamin K deficiency. One box is added to depict causes of vitamin K deficiency. 12 references are given at the end of the chapter for further reading.