This guide introduces and defines the emerging technology of custom power. This technology involves devices and circuit configurations of power electronic equipment used in utility power distribution systems rated 1 kV through 38 kV for the purposes of mitigating problems associated with power quality. This guide also includes definitions, general need guidelines, performance objectives, electrical environments, input/output criteria, performance measurements, case studies, bibliography, and engineering trade-offs. The proposed document addresses power assessment techniques as specified by IEEE Std 1250TM-20111, which defines power quality terms and phenomena, and IEEE Std 1159TM-2009, which provides a recommended practice for measuring power quality.