Acquisition of large bodies of genomic sequence is facilitating the use of global techniques to assay cellular function. DNA microarrays have enabled the measurement of global mRNA levels and are able to detect changes in gene expression between different cellular states. Since much of the regulation of physiological processes happens post-translationally, measuring only the mRNA levels gives an incomplete picture. Strategies to assay global expression, localization, or interaction of proteins fall into the emerging field of proteomics, with various combinations of techniques being utilized to separate and identify proteins. In this review, we will present a general overview of the currently available proteomic tools and then give examples of how these tools are being utilized to answer questions in cell biology.