Tax inversion is a mainly American term for the movement of a company HQ to a lower tax region, whilst still maintaining operations in their home nation. The US imposes income tax on the foreign earnings of American companies. So, by setting themselves up as ‘foreign companies’ by law, these firms can lower their tax obligations but still reap the benefits of access to the US market. The way companies achieve this is to buy an overseas competitor and then make the competitor’s HQ represent the entire legal entity.