In this document, EPA is taking final action on key elements of the program to implement the 8-hour ozone national ambient air quality standard (NAAQS or standard). This final rule addresses the following topics: classifications for the 8-hour NAAQS; revocation of the 1-hour NAAQS (i.e., when the 1-hour NAAQS will no longer apply); how anti-backsliding principles will ensure continued progress toward attainment of the 8-hour ozone NAAQS; attainment dates; and the timing of emissions reductions needed for attainment. We are issuing this rule so that States and Tribes will know how we plan to classify areas and transition from implementation of the 1-hour NAAQS to implementation of the 8-hour NAAQS. The intended effect of the rule is to provide certainty to States and Tribes regarding classifications for the 8-hour NAAQS and their continued obligations with respect to existing requirements. This document is Phase 1 of the program to implement the 8-hour ozone NAAQS. We plan to issue a second rule, Phase 2, within the next several months which will address the remaining 8-hour implementation issues, e.g., requirements for reasonable further progress (RFP), requirements for modeling and attainment demonstrations, and requirements for reasonably available control measures (RACM) and reasonably available control technology (RACT).