A range of tests is available to the physician pursuing the diagnosis of gastroesophageal reflux disease (GERD). Many times, these studies are unnecessary because the history is sufficiently revealing to identify the presence of troubling reflux disease.(1) However, this may not be the case and the clinician must decide which tests to choose to arrive at a diagnosis in a reliable, timely, and cost-effective manner (Table 1). Furthermore, the various esophageal tests need to be selected carefully depending upon the information desired. For example, identifying the presence of gastroesophageal reflux disease is different from proving that the patient's symptoms are caused by reflux episodes. Additionally, defining that acid reflux exists may not be enough. To tailor appropriate medical or surgical therapy requires knowing whether complications of GERD are present as well as possible mechanisms by which abnormal GER occurs. A thorough and well-devised investigation strategy requires knowledge of testing procedures ranging from radiology and pathology to physiology and endoscopy. An informed background in these areas allows the clinician and investigator to address not only the presence of reflux and its correlation to patient symptoms but also the severity of esophageal injury and even the mechanisms by which the damage is done. By using the available tests judiciously, one can increase the opportunity of making a correct diagnosis of GERD and simultaneously limit the potential inconveniences or cost to the patient.