Total-joint replacement is one of the most common and successful operation in orthopedics. These operations are per-formed to relieve pain and restore patient function. Currently, a large variety of new implant designs are offered featuring modular components, surface coatings and complex geometries. Modularity provides surgical flexibility in terms of mate-rial combinations and size selection. These new designs, in general, have biomaterials and geometries that better fit pa-tient anatomy and meet biomechanical requirements of young and active patients. Titanium and its alloys have been used as the biomaterial of choice in the design of modular implants due to a combination of attractive properties. The material has low modulus of elasticity, exhibits excellent biocompatibility and corrosion resistance, and has sufficient strength to withstand static and cyclic stresses on the implant surface. In particular, the alloy Ti6Al4V has been extensively used for the femoral component of artificial hips and the tibial component of knee implants because of its improved fatigue resis-tance. Cobalt based alloys (CoCr/CoCrMo) are vastly used in the design of articulation surfaces of total-joint systems, such as the acetabular component of a hip and the femur of a knee, due to its superior wear, hardness and fatigue resis-tance. New generations of cross-linked ultra-high molecular weight polyethylene (UHMWPE) offering improved wear resistance are also used in the design of articulation interfaces and liners. Alternatively, nearly inert crystalline ceramics (alumina, zirconia) can replace CoCr femoral heads and other articulation components due to their excellent tribological properties, bioinertness, hardness, and good clinical results. Despite the success achieved with this new generation of de-signs and biomaterial combinations, an increase in the number of failed implantations is leading to an increase in the num-ber of revision surgeries. Several clinical reasons can lead to implant malfunction. Typically, failure is associated with mechanical loosening caused by severe corrosion or fatigue processes, dislocation, osteolysis, infection, pain, and peri-prosthetic failure. Modular connections between Ti6Al4V-Ti6Al4V interfaces or Ti6V4Al-CoCr have been recently asso-ciated with severe cases of corrosion inducing metallosis and pseudotumors. Despite its natural protective layer and high corrosion resistance, titanium can be subject to severe degradation in vivo. Better understanding potential mechanisms of in vivo failure is crucial and will enable implant manufactures to improve current designs and materials selection to achieve the required clinical efficacy and safety. In this talk, I will discuss biomaterial technologies in development for performance improvement of orthopedic implants. Particular focus will be given to titanium and cobalt alloys, polyethyl-ene and alumina based bioceramics, and mechanisms of in vivo failure.