The field of diffuse optical imaging has made significant advances since the two reviews of “optical imaging in medicine” were published in Physics in Medicine and Biology in 1997. Imaging systems have become faster, more robust, less susceptible to error, and able to acquire data with more source-detector combinations and at more wavelengths. Images are now routinely reconstructed in 3D, using more sophisticated techniques which can be adapted to the clinical situation by incorporating prior information and by compensating for some of the unavoidable sources of measurement error. The greatest recent progress has probably been in the demonstration of clinical applications: many hundreds of optical breast and brain examinations have now been carried out worldwide.