Tandem Starters are two pitchers who pitch as a pair. The Tandem A start will start the game. The Tandem B pitcher will relieve the Tandem A starter as long as the Tandem A pitcher exits prior to the late innings (typically inning 7). Tandem Pitcher A will go until his pitch count is met or until he's knocked out for performance reasons. Tandem B will also pitch until his pitch count is met or gets knocked out for performance reasons. Beyond that, typical relief pitcher logic is used.
Tandem pitchers exist so owners can combine two pitchers with limited IP (or pitches)/G into a successful starting pitcher tandem.
Regular starting pitchers are not allowed to be entered into the rotation after Tandem starters. Multiple pairs of Tandem starters are allowed in a rotation. Tandem starters cannot be in the same rotation as Swing starters.