This Practice Note provides an introduction to the UK’s rules to counteract hybrid and other mismatches, also referred to as the anti-hybrid rules and some of the key terms used in the legislation. The UK hybrid rules, counteracting deduction/non-inclusion (D/NI) mismatches and double deduction (DD) cases, are found in Part 6A of the Taxation (International and Other Provisions) Act 2010. They replaced the arbitrage rules (also referred to as the anti-arbitrage rules) with effect from 1 January 2017. This Practice Note was produced in partnership with Dominic Robertson of Slaughter and May.