Three-dimensional imaging of osteoarthritis is so far limited to late stages of the disease. In this chapter we introduce microcomputed tomography (microCT) as a new imaging tool that offers exciting features for diagnosis of earlier disease stages and for disease monitoring. microCT provides spatial resolution better than 100 microm, but the size of the objects that can be scanned is restricted to several centimeters. The strength of X-ray-based techniques like micro CT is the excellent visualization of bone. Therefore, the main application of microCT in osteoarthritis (OA) will be the analysis of bone in small-animal models or of human bone biopsies. As an example, we will exemplarily describe the application of microCT for the examination of knee joints of male STR1N mice. This inbred strain spontaneously develops OA that carries many characteristics of the human disease. With microCT it is possible to monitor the prominent bony alterations such as osteophyte formation, trabecular remodeling, subchondral bone plate thickening, and subchondral sclerosis. We discuss sample preparation, scanning procedures, data processing, and analysis as well as implications and restrictions for in vivo and in vitro applications.