The Beltway Series, promoted by the teams as "The Battle of the Beltways," is the Major League Baseball (MLB) interleague rivalry series played between the Baltimore Orioles and Washington Nationals. The Orioles are a member of the American League (AL) East division, and the Nationals are a member of the National League (NL) East division. The series name is taken from the beltway highways, the Baltimore Beltway (I-695) and the Capital Beltway (I-495), that serve Baltimore, Maryland, and Washington, D.C., respectively.

Interleague play in Major League Baseball refers to regular-season baseball games played between an American League (AL) team and a National League (NL) team. Interleague play was first introduced during the 1997 Major League Baseball season. Prior to that, matchups between AL teams and NL teams occurred only during spring training, the All-Star Game, other exhibition games, and the World Series. Unlike modern interleague play, none of these contests, except for the World Series, counted toward official team or league records.