Joe Biden, Paul Ryan

Vice President Joe Biden and Republican V.P. candidate Paul Ryan will debate tonight, the first and only time the two will go head-to-head before next month's election.

The debate will take place at Centre College in Danville, Ky., and will be broadcast live on all the major networks, as well as several cable channels, beginning at 9/8c. As a result, the following shows will be pre-empted: Grey's Anatomy and Scandal on ABC; Person of Interest and Elementary on CBS; The Office, Parks and Recreation, and Rock Center with Brian Williams on NBC; and Glee on Fox.

The debate will be divided into nine 10-minute segments, each covering a foreign or domestic issue. It will be moderated by ABC News correspondent Martha Raddatz.