WWE has been broadcasting PPV events since the 1980s, when its classic "Big Four" events (Royal Rumble, WrestleMania, SummerSlam, and Survivor Series) were first established. The company's PPV lineup expanded to a monthly basis in the mid-1990s before expanding even further in the early-2000s. In March 2007, WWE announced that all subsequent PPV events would feature performers from all brands. In 2008, all WWE PPV events began broadcasting in high-definition.