Bone tissue consists of bone cells surrounded by extracellular matrix. The bone matrix consists primarily of hydroxyapatite, calcium phosphate, and calcium carbonate crystals. The bone cells produce the matrix, and become entrapped within the bone matrix. Other bone cells break down the bone matrix so that new matrix can replace the old matrix. There are four principal types of bone cells:

Osteogenic cells are located in the endosteum, the inner surface of the periosteum, and within haversian canals. They are immature bone cells capable of mitosis that give rise to osteoblasts.

Osteoblasts produce and surround themselves with bone matrix. They are usually found only on the inner surface of the periosteum and are incapable of mitosis.

Osteocytes are mature bone cells that maintain exisiting bone tissue. They are connected to each other through canaliculi. As the osteoblast secretes bone matrix, the cell becomes trapped within lacunae (tiny spaces) at which time they become known as osteocytes. Like osteoblasts, they are nonmitotic.

Osteoclasts are bone-dissolving cells that form by the fusion of monocytes, a type of white blood cell.