The research work presented in this chapter highlights the importance of under- standing the surface chemistry of biomaterials, as well as the main mechanism for apatite formation, which provides the fundamental principles and tools for designing new bioactive materials. These fundamental mechanisms of bioactive ceramics are believed to open a new avenue for future breakthroughs for clinical biointeractive materials with novel physical, chemical, and biological functions. Here, it was demon- strated that any organic polymer can also exhibit bioactivity if its surface is modified with a functional group effective in apatite nucleation. These new types of bioactive materials are expected to play an important role in bone replacement and regeneration. Therefore, it can be concluded that the key point lies in designing an organized func- tionalized surface to control the mechanisms of apatite nucleation. Additionally, we highlight that controlling the material properties by functionalization can work as an approach to control cell proliferation and differentiation.