Hybrid composites based on inorganic hydroxyapatite (HAp) and biodegradable polymers have a high and increasing potential for biomedical applications. In fact, HAp is among the most important implantable materials due to its biocompatibility, bioactivity, and osteoconductivity. Multiphase materials can be engineered to combine the advantages exhibited by each component (inorganic and organic) and provide structures with properties and composition similar to those found in the nature. The first sections of the chapter are focused on the different synthetic approaches that can be applied to prepare nano-hydroxyapatite (nano-HAp) crystals with controlled morphology and the procedures that allow to get composites based on nano-HAP and biodegradable polymers of natural or synthetic origin. Last sections are devoted to highlight the attractive properties and applications of systems based on HAp. Specifically, the formation of complexes with DNA as nonviral gene carriers, the development of biodegradable scaffolds for tissue engineering, which can also be designed to provide a sustained release of growth factors and drugs, and finally the development of new nanohydrogels and nanostructurated coatings.