This guide describes performance, functional, and communication needs of phasor data concentrators (PDCs) for power system protection, control, and monitoring applications. The guide covers synchrophasor system needs and testing procedures for PDCs. It includes functional requirements for associated interfaces with phasor measurement units (PMUs) to a PDC and PDC systems. In particular, it includes requirements for synchronization, synchrophasor data processing, and real-time access.