With the ultimate goal of systematically identifying and characterizing proteins within an organism, the field of proteomics has generated much excitement in the past few years. Coupled with mass spectrometry, various quantitative and functional techniques are now available that allow for large-scale analyses of proteins implicated in cancer. New techniques are just now being applied to identifying the temporal changes in protein levels associated with tumor development. This review will focus on the use and promise of proteomic technologies as they apply to the study of tumor progression and metastasis.