This document lists the requirements for accurate time in Power Systems. This need is driven by Synchrophasors and the SCADA system. The Precision Time Protocol (PTP), defined by IEEE 1588, is described, including the features which allow it to deliver the required time transfer accuracy. The IEEE Power and Energy Society sponsored the creation of IEEE C37.238-2011, a PTP profile for the Power Industry. The profile describes constraints on the use of PTP to make sure that Power Systems meet their timing requirements. This profile is described in this document.