Clear Channel Outdoor Holdings is one of the world's largest outdoor advertising companies. The company is engaged in providing advertising opportunities through billboards, street furniture displays, transit displays, and other out-of-home advertising displays for its clients. Clear Channel's traditional billboard advertising is the largest revenue source for the company, although the company is aggressively expanding its use of digital billboards and displays. Clear Channel advertisements are located in most of the largest United States markets, as well as over 30 countries around the world. The company's revenue breakdown between the United States and international markets is approximately even.