The process of bone formation is crucial for different processes including bone remodeling, bone mineralization, and the longitudinal growth of bones. The composition of bone includes progenitor cells, osteoblasts, osteoclasts, and osteocytes. The presence of contaminant blood-derived cells, endothelial cells, and pericytes should not be disregarded as potential sources of osteoprogenitor cells. Osteoblasts have a vital function in the synthesis of extracellular matrix components. Osteoclasts are derived from the macrophage/monocyte lineage. Osteocytes are unique cells that express genes from both the hematopoietic and mesenchymal lineages. To effectively employ osteoprogenitor cells for novel treatments, it is imperative to actively extract them from tissue samples, specifically from skeletal muscles. Furthermore, several transcription factors are involved in the processes of differentiation and inhibition of bone cells. Programmed cell death also has a crucial function in cellular processes. In order to design appropriate implants, it is crucial to know the reasons and mechanisms of cell death. The interactions between bone tissue engineering materials and these cells should be considered. A comprehensive understanding of bone components is invaluable when designing and producing bone tissue engineering devices. This chapter will comprehensively consider these cells and the mechanisms that regulate them.