The Australian twenty cent piece was first put into circulation with the introduction of decimal currency in 1966 and continues to be used in circulation today. During these years three standard types have been issued, the first (1966 - 1984) featured the Arnold Machin portrait of HM Queen Elizabeth II, the second (1985 - 1998) featured the Raphael Maklouf portrait, and the third (1999 - Present) features the Ian Rank-Broadley portrait. A number of additional non-circulating types outside of these years have also been produced, particularly as part of the Masterpieces in Silver collection. Despite the changes to the obverse, the reverse of these three types has remained the same Platypus design by Stuart Devlin.
In addition to the three main types the Royal Australian Mint has produced a large variety of commemorative twenty cent pieces. These pieces typically feature the same obverse portraits as the standard types (although not always) with an alternative reverse design issued to mark significant events, people, or organisations.