Clean Water Act (CWA) section 401 provides States and Tribes with a powerful tool to protect the quality of their waters from adverse impacts resulting from federally licensed or permitted projects. Under section 401, a federal agency may not issue a license or permit to conduct any activity that may result in any discharge into navigable waters, unless the State or Tribe where the discharge would originate either issues a section 401 water quality certification finding that any such discharge will comply with the applicable provisions of sections 301, 302, 303, 306, and 307 of the CWA, or waives certification. EPA promulgated implementing regulations for water quality certification prior to the passage of the CWA in 1972, which created section 401. EPA revised the regulation in 2020. In June 2022, consistent with Executive Order 13990, EPA proposed Clean Water Act Section 401 Water Quality Certification Improvement Rule” to revise the 2020 Rule. This rule updates the existing regulations to better align with the statutory text and purpose of the CWA; clarifies, reinforces, and provides consistency with practice over the 50 years since the 1971 Rule was promulgated. The rule supports an efficient and predictable certification process that is consistent with the water quality protection and cooperative federalism principles central to CWA section 401.