American Tower Corporation is a publicly held company, owner and operator of wireless and broadcast communications infrastructure in several countries. American Tower is headquartered in Boston, Massachusetts and has local offices worldwide. The company was formed in 1995 as a unit of American Radio Systems, and was spun off from that company in 1998 when that company merged with CBS Corporation. Following the merger, American Tower began international expansion by establishing operations in Mexico in 1998 and Brazil in 1999. The company is structured as a real estate investment trust.