Gastrointestinal (GI) infections are a major cause of morbidity and mortality worldwide. Although infectious organisms are often recovered by microbiological methods, surgical pathologists play an invaluable role in diagnosis. The lower GI tract, including the appendix, large bowel, and anus, harbors a wide variety of pathogens. Some infections are part of disseminated disease, whereas others produce clinicopathologic scenarios that are specific to the lower GI tract. This review focuses on selected infectious disorders of the lower GI tract that may be encountered by the general surgical pathologist, including viral, bacterial, fungal, and parasitic organisms, and including infections caused by food- and water-borne pathogens. Diagnostic gross and histologic features are discussed, as well as useful clinical features and ancillary diagnostic techniques. Pertinent differential diagnoses are also emphasized, including other inflammatory conditions of the gut (such as ischemia or idiopathic inflammatory bowel disease) that can be mimicked by lower GI infections.