This guide provides the functional requirements for unified power flow controller (UPFC) deployment@ including application conditions@ system architecture@ function requirements@ performance requirements@ primary equipment requirements@ control and protection requirements@ auxiliary system requirements@ testing@ spares@ as well as training of UPFC projects@ which are suitable for UPFC in transmission power grids. Purpose The purpose of this guide is to specify the functional requirements for UPFC project application@ therefore utilities@ integrators@ and other interested entities can specify the application conditions and system architecture of UPFC@ and define the requirements for function@ performance@ primary equipment@ control and protection@ commissioning and testing of UPFC projects. This guide aims to provide the knowledge base@ experience@ and opportunities for greater utilization of UPFC.