The Environmental Protection Agency is issuing regulations to implement certain provisions of the American Innovation and Manufacturing Act, as enacted on December 27, 2020. This Act mandates the phasedown of hydrofluorocarbons, which are highly potent greenhouse gases, by 85 percent over a period ending in 2036. The Act directs the Environmental Protection Agency to implement the phasedown by issuing a fixed quantity of transferrable production and consumption allowances, which producers and importers of hydrofluorocarbons must hold in quantities equal to the amount of hydrofluorocarbons they produce or import. To establish the allowance allocation program, this rulemaking determines the hydrofluorocarbon production and consumption baselines, from which allowed production and consumption will decrease consistent with the statutory phasedown schedule; provides an initial approach to allocating calendar-year allowances and allowing for the transfer of those allowances; establishes provisions for the international transfer of allowances; and establishes recordkeeping and reporting requirements. Additionally, it establishes provisions to support implementation, compliance with, and enforcement of, statutory and regulatory requirements under the Act's phasedown provisions. Over the time period from 2022-2050, this rulemaking will avoid cumulative emissions of 4,560 million metric tons of exchange value equivalent of HFCs in the United States with a present value of cumulative net benefits of $272.7 billion.