Constitution Day in Australia is observed annually on July 9, commemorating the approval of the Constitution of Australia in 1900. Although it is not a public holiday, it is a popular observance that was introduced in 2000 to mark the centenary of the Constitution. The commemoration saw a decline in participation after 2001 but was revived in 2007, organized by the National Archives of Australia, where the original Constitution document is preserved, and the Department of Immigration and Citizenship. The Constitution consists of several documents, with the most significant being the Constitution of the Commonwealth of Australia, which became law on July 9 and took effect on January 1, 1901. In 1986, the United Kingdom parliament removed its power to amend the Constitution, allowing changes only through prescribed referendum procedures.