Politicians and campaigners are fond of saying that companies should pay their ‘fair share’ of tax, but the phrase is over-used and lacks legal meaning and backing, becoming little more than a cliché. However, new research has identified clauses in the Constitutions of 15 countries – including two of the G7 member states – which identify an obligation to contribute to the public purse. Joe Stanley-Smith explores how this could force companies to take more notice of the fair-share debate.