Chemical weapons are prohibited, however recent chemical weapons attacks in Malaysia, Syria, Iraq and the UK have raised concerns about their use. In the UK in 2018, four people were taken seriously ill and one person died following exposure to a Novichok, a type of nerve agent. The UK Government recently announced £11m to strengthen the UK's chemical defences and highlighted chemical, biological, radiological and nuclear (CBRN) threats as an area of focus in the recent Modernising Defence Programme. This briefing provides an overview of chemical weapons including types of chemical weapons and modes of delivery, chemical weapons control and disarmament, investigations of alleged attacks and chemical weapons defence in the UK.