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Salmonella enterica serovar Typhimurium (aka, S. typhimurium) is a facultative intracellular pathogen that causes ~40,000 reported cases of acute gastroenteritis and diarrhea each year in the United States. While many successful physiological, biochemical, and genetic approaches have been taken to determine the key virulence determinants encoded by this organism, the shear number of uncharacterized reading frames observed within the S. enterica genome suggests that many more virulence factors remain to be discovered. We have used a liquid chromatography-mass spectrometry-based “bottom-up ” proteomics approach to generate a more complete picture of the gene products that S. typhimurium synthesizes under typical laboratory conditions, as well as in culture media that are known to induce expression of virulence genes. When grown to logarithmic (log) phase in rich medium, S. typhimurium is known to express many genes that are required for invasion of epithelial cells. Conversely, stationary phase cultures of S. typhimurium express genes that are needed for both systemic infection and growth within infected macrophages. Lastly, bacteria grown in an acidic, magnesium-depleted minimal medium (MgM