Improving Spectrum Coordination Act of 2021 This bill requires the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) to periodically update the Memorandum of Understanding on Spectrum Coordination, which establishes procedures to promote the efficient use of the radio spectrum, including related to joint spectrum planning and frequency coordination. Among other updates, the FCC and the NTIA must (1) outline processes for addressing technical, procedural, and policy differences regarding frequency allocation and related conditions and standards; (2) create a process for the resolution of nonroutine policy disputes; (3) clarify the role of the NTIA; and (4) outline processes for spectrum planning and international spectrum coordination.