Abstract The ability to measure biochemical and molecular processes underlies progress in breast cancer biology and treatment. These assays have traditionally been performed by analysis of cell culture or tissue samples. More recently, functional and molecular imaging allows in vivo assay of biochemistry and molecular biology that is highly complementary to tissue-based assay. Molecular imaging can serve and number of roles, from characterization of pre-clinical models, to testing the ability of novel drugs to interact with their intended targets, to characterizing entire burden of disease for patients with breast cancer, to helping direct therapeutic choices and assign their efficacy. This talk will review basic principals of molecular imaging, with an emphasis on those methods of greatest translational potential. The session will discuss the use of pre-clinical models of breast disease to help test and validate new molecular imaging methods, and in turn, the use of molecular imaging to characterize the disease process in the animal models. The session will then review the current state of molecular imaging in breast cancer patients, including methods in routine clinical use, those undergoing advanced clinical trials, and those in early-phase testing. The session is designed for a broad audience, ranging from breast cancer translational scientists to practicing physicians caring for breast cancer patients.