Optical mammography is one of several new techniques for breast cancer detection and characterization presently under development for clinical use that provide information other than morphologic, in particular on the biochemical and metabolic state of normal and diseased tissue. In breast tissue, scattering of red to near infrared (NIR) light dominates absorption and NIR light may penetrate several centimeters through the breast. Optical mammography avoids the use of ionizing radiation and offers the power of diffuse optical spectroscopy. However, because of strong light scattering, spatial resolution of optical mammography is generally low. The paper reviews the results of a clinical study on scanning time-domain optical mammography comprising 154 patients carrying a total of 102 carcinomas validated by histology. Ninety two of these tumors were detected in optical mammograms retrospectively and for 87 of the detected tumors optical properties and tissue parameters were derived. In addition developments on instrumentation and data analysis are covered and possible improvements of optical mammography are briefly discussed.