The Australian 20 cent coin was first introduced with decimalisation on 14 February 1966 when it replaced the pre-decimal Australian florin, to which it is equal in size and mass. The original reverse design by Stuart Devlin has not been changed since its introduction.
The denomination is occasionally used by both the Royal Australian Mint and the Perth Mint to issue collector coins, which are legal tender in Australia - such as this one.
In 2006, the Royal Australian Mint produced some for mint sets (brilliant uncirculated coins and proofs), celebrating the 40th anniversary of the decimal currency. The silver proofs (only) have Her Majesty's "Second Portrait" (by Arnold Machin), which was last used in Australia in 1984.
The 8-coin Fine Silver Proof 2006 Year Set contains 1 cent, 2 cents, 5 cents, 10 cents, 20 cents, 50 cents (round), $1 and $2 coins - all with the Queen's Second Portrait by Arnold Machin, as the initial decimal coins released in 1966.
The coins were made of 99.9% silver. No coins of this type were released into circulation. | 
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