The U.S. Nuclear Regulatory Commission (NRC) is issuing Revision 1 to Regulatory Guide (RG) 4.2, Supplement 1 (RG 4.2S1), "Preparation of Environmental Reports for Nuclear Power Plant License Renewal Applications." This regulatory guide provides guidance to applicants in the preparation of environmental reports that are submitted with the application for the renewal of a nuclear power plant operating license. Applicants should use this regulatory guide when preparing an environmental report for license renewal to ensure that the information they submit to the NRC is complete and facilitates the NRC staff's review.