成骨作用指硬骨的生成，过程主要是以软骨为主的结缔组织被骨细胞取代，并引起血管新生，带来钙离子以利硬骨细胞合成骨质。成骨的过程又基于生长的模式分为：软骨内骨化、膜内骨化。

Ossification (or osteogenesis) in bone remodeling is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the formation of normal, healthy bone tissue: Intramembranous ossification is the direct laying down of bone into the primitive connective tissue (mesenchyme), while endochondral ossification involves cartilage as a precursor. In fracture healing, endochondral osteogenesis is the most commonly occurring process, for example in fractures of long bones treated by plaster of Paris, whereas fractures treated by open reduction and internal fixation with metal plates, screws, pins, rods and nails may heal by intramembranous osteogenesis.