Diffuse optical tomography (DOT) is emerging as a viable new biomedical imaging modality. Using near‐infrared (NIR) light, this technique probes absorption as well as scattering properties of biological tissues. First commercial instruments are now available that allow users to obtain cross‐sectional and volumetric views of various body parts. Currently, the main applications are brain, breast, limb, joint, and fluorescence/bioluminescence imaging. Although the spatial resolution is limited when compared with other imaging modalities, such as magnetic resonance imaging (MRI) or X‐ray computerized tomography (CT), DOT provides access to a variety of physiological parameters that otherwise are not accessible, including sub‐second imaging of hemodynamics and other fast‐changing processes. Furthermore, DOT can be realized in compact, portable instrumentation that allows for bedside monitoring at relatively low cost. In this paper, we present an overview of current state‐of‐the ‐art technology, including hardware and image‐reconstruction algorithms, and focus on applications in brain and joint imaging. In addition, we present recent results of work on optical tomographic imaging in small animals.