The material in this paper is different from the mainstream topics in this summer's International School of Physics “Enrico Fermi”. It should become apparent, however, that the roots of these biomedical optics research problems share common features with much of the light scattering and transport research taught in the Varenna summer school. Here, our intention is to provide an informal review that establishes the roots of diffuse optics, and then demonstrates how diffuse optics is finding application in medicine. This paper will have two main themes. After a brief motivation of the problem, the first theme will provide a coherent discussion about light transport in turbid media. The second theme is oriented towards problems in biomedicine. As such, a short discussion of hemodynamics will be followed by representative current work from our lab, particularly with breast and brain.