P25 received its name under APCO’s tradition of numbering its broad initiatives that affect the public safety communication world. “P25” has become synonymous with “public safety digital radio standards.” Three key aspects of P25 make it important for improved communication interoperability, i.e., the capacity of different public-safety agencies to have radio communication with one another. First, the P25 standards initiative was begun and driven by public safety agencies and organizations. Second, P25 proceeded with both a vision of forthcoming technological change and the need for the smooth migration between technologies used by public safety agencies. Third, competition based on open standards would produce the best technology at the best prices for public safety agencies. P25 defined a general system model for public safety radio communications with eight open interfaces. These interfaces connected components (subsystems) of radio systems that were becoming increasingly complex year after year. This paper describes these interfaces. P25’s value for interoperability is twofold. First, it harnesses the naturally disruptive trend of technological change; and second, it requires backward compatibility, i.e., radios built to P25 standards would be technically capable of communicating with earlier analog radios, including within trunked systems. This paper discusses when P25 is required, its value to an individual agency, and its disadvantages (cost, conventional use and interference, and complexity that breeds incompatibilities). The current status and future of P25 are also discussed. 1 figure