As market-based instruments, emissions trading systems are inherently flexible, as entities can decide to reduce their own emissions or buy emissions allowances from the market. Carbon offsets (or simply ‘offsets’) are a tool to further increase flexibility in reaching climate targets under ETSs, as they offer sectoral and geographical flexibility for jurisdictions to reduce greenhouse gas emissions outside of the scope of their ETS. This report gives an overview of offset provisions in several major ETSs around the world and provides an outlook for offsets in the years to come.