The Current Procedural Terminology (CPT) code set is maintained by the American Medical Association through the CPT Editorial Panel. The CPT code set accurately describes medical, surgical, and diagnostic services and is designed to communicate uniform information about medical services and procedures among physicians, coders, patients, accreditation organizations, and payers for administrative, financial, and analytical purposes. The current version is the CPT 2019.
Category I codes are used for reporting services or procedures performed by physicians and other healthcare providers, tests and drugs (including vaccines) required for the performance of a service or procedure.
Category II codes are used for reporting performance measures reducing the necessity for chart review and medical records abstraction.
Category III codes are used for reporting emerging technology in a number of capacities including services or procedures recently performed on humans, clinical trials and etc.
2004 Introduction of Category III codes that end with T (temporary codes for emerging technologies)
2005 Introduction of Category II codes that end with F (used for supplemental tracking for performance measurement)
2010 The AMA changed the method of only "grouping" or "relating" codes for similar procedures, and instituted the use of codes from other sequences, these codes became known as resequenced codes
2015 Multianalyte Assays with Algorithmic Analysis (MAAA) codes end with M (in Appendix O)
2017 Proprietary laboratory analyses codes end with U, in the Pathology and Laboratory section (this category comes after code 89398)
CPT is currently identified by the Centers for Medicare and Medicaid Services (CMS)  as Level 1 of the Health Care Procedure Coding System.
CPT is a registered trademark of the American Medical Association. The AMA holds copyright which prevents free use and distribution of codes.
Although the CPT system is mandated by the Centers for Medicare and Medicaid Services (CMS) and HIPAA, and the data for it appear in the Federal Register, the American Medical Association (AMA) maintains that their copyright of the CPT allows them to charge a license fee to anyone who wishes to associate Relative Value Unit (RVU) values with CPT codes. The AMA receives approximately $70 million annually from these fees, making them reluctant to allow the free distribution of tools and data that might help physicians calculate, record, or submit their fees accurately and fairly.