This chapter focuses on calcium in the context of dietary sources and providing bases of calcium metabolism in the human body. Calcium is an inorganic element essential to living cells present in the Earth's biosphere as a solid matter and aqueous solution. In humans, calcium is an essential constituent of bones and teeth where it supports structure. It is a key component of vascular calcification, and is necessary for activation catalytic and mechanical properties of proteins in key enzymes. Dietary sources of calcium include dairy and nondairy foods, fortified foods and supplements such as calcium carbonate and calcium citrate. Calcium is readily absorbed through the gastrointestinal tract by way of vitamin D3 action. Calcium forms complexes with some food components and this allows it to be absorbed alongside the food molecules. High gastric acidity also aids solubilization and absorption of calcium salts such as carbonate, sulfate, fluorite, and phosphate. In a neutral environment, the absorbability of calcium is influenced by other food components such as lactose, glucose, fatty acids, phosphorus, and oxalate that can bind to soluble calcium. Calcium balance is measured as the difference between the calcium absorbed and that which is excreted, for example in urine, feces and sweat. It is essential to maintain this balance in order to facilitate many physiological processes, ranging from cell signaling to maintenance of bone health. Calcium homeostasis is regulated by the interrelationship between intestinal calcium absorption, bone influx and efflux of calcium, and renal calcium excretion.