Evaluating patients with gastrointestinal (GI) illness involves the use of many different diagnostic modalities, including laboratory studies, diagnostic imaging, and endoscopy. Rapid advances in all three areas have provided clinicians with a wide array of testing at their fingertips. The frequent challenge in evaluating a patient is deciding which testing will lead to a diagnosis in the most direct and efficient manner. This article reviews many of the tests that are considered in the evaluation of individuals with complaints referable to the GI tract.