Vitamin B, often referred to as the vitamin B complex, encompasses a group of water-soluble vitamins that play crucial roles in various physiological processes essential for human health. This chapter provides a comprehensive overview of the individual B vitamins, including thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (B12). Each vitamin is discussed in detail, covering its biochemical functions, dietary sources, recommended intake, metabolism, and associated health benefits. Emphasis is placed on the synergistic interactions among the B vitamins and their involvement in energy metabolism, DNA synthesis, red blood cell formation, neurotransmitter synthesis, and maintenance of neurological function. Furthermore, the chapter explores the consequences of B vitamin deficiencies, ranging from fatigue and weakness to severe neurological disorders and birth defects.