Single-phase components (also called monolithic) do not always provide all the properties necessary for a given application, which leads to the concept of composites. For better understanding, the relationship between stiffness and strength of some of the widely used biomaterials are shown in Figure 9.1 (Mano et al. 2004). It can be seen from the gure that metals and ceramics are stiffer and possess higher strength than biological hard tissues, whilst polymers mostly possess lower modulus and can have strengths of the same order of magnitude as hard tissues. It should be noted that biological hard tissues exhibit larger spectra of mechanical properties than the monolithic biomaterials. Therefore, there is a need for compounding various monolithic biomaterials in order to obtain composite biomaterials that have mechanical properties quite similar to those of biological hard tissues. It is also noted that the mechanical and biological properties of the hydroxyapatite (HA)/ collagen composites are better than their constituents and quite similar to biological hard tissues. Thus composites are a better choice for a variety of biomedical applications than the monolithic biomaterials. In addition, there is a possibility of tailoring their properties better than their each constituent, and to eliminate or minimize the problems associated with the monolithic biomaterials. These facts greatly increase the use of composites in a variety of biomedical applications.