Endodontics is concerned with the prevention and treatment of diseases and injuries of the pulp and associated periradicular conditions. It is critical that an accurate diagnosis is made prior to any treatment. Each clinician will use their knowledge, experience as well as results of diagnostic tests to formulate an individual treatment plan for the patient. On occasion, it is not possible to elicit test results that pinpoint a definitive diagnosis. At best it may only be possible for the clinician to provide a list of possible differential diagnoses. More advanced technology may help the clinician gain additional information on which to base treatment decisions. This article will review the materials and instruments required to perform diagnostic tests for establishing a baseline. In addition, more advanced diagnostic tests will be reviewed.