The Rapid Environmental Impact Assessment in Disaster (REA) is a tool to identify, define, and prioritize potential environmental impacts in disaster situations. It is based on a simple, consensus-based qualitative assessment process, involving narratives and rating tables, which are used to identify and rank environmental issues and follow-up actions during a disaster. This document provides the guidelines for the REA, which is composed of five main parts and ten supporting Annexes. The main parts include an Introduction to the REA, and modules on Organization and Community Level Assessments, Consolidation and Analysis of assessment results and Green Review of Relief Procurement. The Annexes include information sources, forms used in the assessment and information useful in managing the REA process. Additionally this guidelines document provides a comprehensive description of the REA process together with background information on key tasks needed to complete the assessment. A separate Quick Guide to the REA process is also available, which includes the rating forms and instructions found in the Guidelines but only a minimal amount of additional information on the REA process.