Niue, a sovereign state in free association with New Zealand, uses two official legal tender currencies. The New Zealand Dollar is the circulation currency for daily transactions, while the government also authorises legal tender coins in the Niue Dollar currency for collector's purposes.
A number of mints issue a large variety of commemorative, bullion and collector coins under the authority of Niue. These coins are dedicated to historical or general popular culture themes not related to Niue itself. Many of them are made using "smartminting" techniques and have features not generally found in circulation coins - e.g. high relief, full colour printing and/or different forms, including fully three dimensional (3D).
Some coins are marketed in standard bullion sizes, like half ounce silver, one ounce silver etc, and some of those are also denominated as $1, for which see respective lists; this particular coin denominated as One Niue Dollar is not in a standard ounce-based size.
This commemorative coin was issued to celebrate the engagement of Prince William of the United Kingdom and Catherine Middleton, which was announced on 16 November 2010.
Their wedding took place on 29 April 2011 at Westminster Abbey in London, United Kingdom. The groom, Prince William, is second in the line of succession to the British throne. The bride, Catherine Middleton, had been his girlfriend since 2003. | 
Search for Niue: One Dollar 2011 Royal Wedding on eBay 