This chapter describes the methodology and a detailed protocol for the targeting and optical imaging of experimental brain tumors in rats using quantum dots (QDs). QDs are optical semiconductor nanocrystals that exhibit stable, bright fluorescence over narrow, size-tunable emission bands. The size-tunable optical properties of QDs allow multiplexing with multiple emission wavelengths from a single excitation source. QDs may be linked to antibodies, peptides, and nucleic acids for use as fluorescence probes in vitro and in vivo. We have hypothesized that the intravenous injection of QDs may represent a novel technique to optically label brain tumors, potentially leading to improved techniques for surgical biopsy and resection.