On 1 January 1901 six separate colonies federated to become the Commonwealth of Australia. At midday on that day, a ceremony in Centennial Park in Sydney was attended by thousands of citizens. A hundred years later in 2001, the nation celebrated its centenary, which provided a focus for Australians and Australians overseas to reflect on the achievements of the nation and its future potential.

The inauguration of the Commonwealth on 1 January 1901 was celebrated by the swearing in of the first Governor-General and the first federal ministry, proclamation of the Commonwealth, and the raising of the new flag. The ceremony included the reading of the Queen's message and the singing of the National Anthem. The Governor-General was sworn in by the Chief Justice of New South Wales and the members of the first federal ministry were sworn in by the Governor-General. The Duke of Cornwall and York (later George V) on behalf of King Edward VII.

• Cover design: Australia Post Design Studio
• Australian stamps: Australia Post Design Studio
• Cover photograph: National Library of Australia
• Centenary of Federation logo: Commonwealth of Australia

This envelope is prepaid for one posting to any destination within Australia, delivered by ordinary post as defined by Australia Post. When posted in Australia, the envelope is not valid for posting to an overseas destination. When posted overseas, the envelope is not valid for posting to an Australian address. This envelope is not exchangeable for cash or for any other postal product or service. Australia Post will not be liable for any loss or damage or inconvenience that may result from the use of this envelope or its contents.