Endodontics is the art of saving teeth by the prevention and treatment of diseases and injuries of the pulp and associated periradicular conditions. To ensure the highest probability of success, it is critical that an accurate diagnosis be made prior to treatment. A systematic process incorporating the information provided by the patient, as well as appropriate diagnostic tests performed by the clinician, combined with the knowledge and experience of the dental practitioner will result in a quick and accurate diagnosis. Only then can a treatment plan best suited to the individual be presented. This article will review the materials and instruments required to perform diagnostic tests for establishing a baseline to an accurate and complete diagnosis.