Artificial hip joints are remarkable bearings to replace diseased or damaged natural hip joints. The successful clinical function of these bearings depends on the tribology of the bearing surfaces. A brief introduction to artificial hip joints will be followed by a detailed review of both the biotribology of the bearing surfaces and the biological responses to the wear debris for evaluating their performances. Various types of artificial hip joints with different bearing surfaces and designs will be considered, including ultra high molecular weight polyethylene against metal or ceramic; metal-on-metal and ceramic-on-ceramic. Future developments of artificial hip joints will also be discussed.