This guide includes criteria, definitions, and test objectives for evaluating the dynamic performance of excitation control systems as applied by electric utilities. The term "excitation control system" (see Fig 1) is used to distinguish the combined performance of the synchronous machine, power system, and excitation system from that of the excitation system alone (see IEEE Std 100-1988, IEEE Standard Dictionary of Electrical and Electronics Terms (ANSI) [1]1 and IEEE Std 421.1-1986, IEEE Standard Definitions for Excitation Systems for Synchronous Machines (ANSI) [2]). The primary purpose of this guide is to provide a basis for evaluating closed-loop performance of excitation control systems for both large and small signal disturbances; confirming the adequacy of mathematical models of excitation control systems for use in analytical studies of power systems; identifying objectives for tests of excitation control systems and their components; and preparing excitation system specifications and additional standards. Portions of this guide will also serve as educational material for people who are becoming acquainted with excitation control systems. Traditionally, large signal performance (see 2.1) has been more closely associated with equipment specification and acceptance testing, while small signal performance (see 2.2) has been more closely associated with stability and model studies. Matching actual disturbance data with model simulations requires that both large and small signal performance criteria be considered during design specification and acceptance testing.