Salmonella is a leading cause of food-borne illness, causing an estimated 1.4 million human cases of Salmonella enteritis annually in the United States, and hundreds of millions of cases worldwide. Children, the elderly, and immune compromised individuals are at high risk to develop Salmonella bacteremia which can be fatal. Despite the importance of this pathogen and over 30 years of study, much of the genome and biology of this organism remains incompletely understood and unexplored. We identify Salmonella genes needed during infection of model and natural hosts using genetics and determine their molecular function using a range of methodologies.