This document describes the first version of the Read-Across Assessment Framework (RAAF) developed by ECHA as an internal tool for examining predictions, based on read-across, of the human health, environmental fate and environmental hazard properties of chemical substances in the context of the REACH Regulation. The aim of this document is to present the concept and principles underpinning the RAAF. The RAAF provides a framework and principles for scientifically examining a read-across case, as well as setting out the critical scientific elements of a read-across case to be assessed. However, the RAAF does not cover all scientific issues or cases, and expert judgement must be used when applying this framework. It is emphasised here that the RAAF focuses on the scientific aspects of the examination of read-across approaches and is intended to be used by experts. This document does not address the way the RAAF is implemented in ECHA’s processes nor does it describe how the shortcomings identified in the scientific assessment are evaluated in the course of dossier evaluation under REACH.