As electrical grids evolve through the introduction of additional “smart” sensors, actuators, and control systems, cybersecurity becomes an ever more significant factor, necessitating the incorporation of Information Assurance principles throughout the electrical system-from central station power generating facilities, through transmission and distribution systems, to building management systems, distributed generation, home area networks, and plug-in hybrid electric vehicles. A precursor to determining the appropriate controls for any particular device within this complex system is to determine the trust model (or untrusted condition) within which the device exists. This paper, then, sets out to define a multilevel framework for an architecture to be used throughout the electrical system-a High-Assurance Smart Grid architecture that incorporates three core attributes: 1) categorizes cybersecurity requirements based on a multi-tier determination of a subsystem's potential impact on the overall system; 2) implements a robust defense-in-depth cybersecurity architecture; 3) implements a distributed rather than hierarchical control system architecture based on an assumed compromise (untrusted condition) of system control components and subsystems using autoresponsive (AR) load control wherever possible.