The UK’s rules on hybrid and other mismatches (referred to in this Practice Note as the hybrid rules) have applied since 1 January 2017 and aim to counteract tax mismatches that arise from the way in which a hybrid instrument or a hybrid entity is treated for tax purposes. Although the hybrid rules normally apply to cross-border transactions involving two or more jurisdictions, they can also apply to purely UK domestic transactions. Specifically, the hybrid rules target: • deduction/non-inclusion mismatches (D/NI mismatches), ie where a payment under a hybrid mismatch arrangement is deductible in the payer jurisdiction for tax purposes but not included in the taxable income of a payee or a related party investor, and • double deduction cases (DD cases), ie where a payment under a hybrid mismatch arrangement gives rise to more than one tax deduction For more information on the hybrid rules, see Practice Note: Hybrid mismatches—introduction to the rules. For an overview in table format of the conditions required by each chapter before any counteraction can apply, see: UK rules