This Practice Note covers the classification system for chemical substances and mixtures under Regulation (EC) No 1272/2008 on Classification, Labelling and Packaging of Substances and Mixtures (CLP Regulation), including the definition of substance and mixture, the level of hazard under the CLP Regulation, impact of classification on the supply chain, who is responsible for classification, when classification is triggered, self-classification and harmonised classification, classification of mixtures, the weight of evidence approach, and who is responsible for receiving information. It was produced in partnership with Begonia Filgueira, Partner at Acuity Law and MD at ERIC Ltd. This Practice Note also links to related Brexit content and information on the position under the Northern Ireland Protocol.