The leading cause of death in human patients with malignant cancer is the dissemination of the primary tumor to secondary sites throughout the body. It is well known that cancers metastasize to certain tissues (e.g. breast cancer typically spreads to the lungs. brain and bone), in a pattern that cannot be explained by blood flow from the primary tumor or simple mechanical arrest. Circulating tumor cells usually arrest in the microvasculature of target tissues. At these sites, they must adhere to the endothelium, survive, proliferate and extravasate in order to form a secondary tumor. In vitro tools that appropriately mimic the microvasculature in which cancer metastasis occurs have been largely unavailable. With the advent of microfluidic and nanotechnology, we can now more accurately model the-complexity of the microvascular environment, in terms of representative endothelial cells, geometry, shear stress and exposure to organ-specific environmental cues. This talk will focus on the use of microfluidic devices to explore mechanisms involved in tumor-endothelial cell interactions that govern cancer metastasis to organ specific sites.