The Australia A-League, established in 2004, is the top professional soccer league in Australia. It replaced the National Soccer League and has since become a popular competition in the country. The league consists of 12 teams, with each team playing a total of 26 matches in the regular season. The most successful teams in the history of the A-League are Sydney FC and Melbourne Victory, both having won the championship four times. An interesting fact is that the A-League was the first professional soccer league in the world to use video assistant referees (VAR) on a full-time basis.