This chapter summarises the requirements of relevant legislation and regulations referring to hazardous substances in the workplace, as well as Health and Safety Executive (HSE), TUC and union guidance on their practical application. It outlines what reps need to know about the Control of Substances Hazardous to Health Regulations 2002 (COSHH). These regulations set out how employers should prevent or control the hazards arising from harmful substances and agents including chemicals, diesel fumes, silica and other dusts.