European Exchange Rate Mechanism
Ireland and the United Kingdom decimalised their currencies in 1971, and parity between the two currencies continued until Ireland joined the European Exchange Rate Mechanism in 1979. An exchange rate between the Irish pound and the pound sterling was established on 30 March 1979. The smaller denomination British 1p and 2p coins continued to be unofficially interchangeable with the Irish coins until the euro was introduced in 2002, partly due to their identical size and shape.