OTB may refer to:

Arts

• On the Boards, an arts organization in Seattle, Washington
• Out of the Blue (American band), a jazz ensemble

Computing

• One True Brace, a software coding convention for formatting loops, functions, if statements, and blocks
• Orfeo toolbox, an open source library for remote sensing image processing
• OTA Bitmap, an image file specification for mobile phones (*.otb files)

Sports and games

• Off-track betting, sanctioned gambling on horse racing outside a race track
• Over-the-board, in chess, played on a single physical chessboard (as opposed to correspondence or online chess)
• Off the ball, in association football, a player's movement when not in possession of the ball

Other

• Off the boat, a slang phrase for newly arrived immigrants
• Overberg Test Range, or Overberg Toetsbaan, a missile test range in South Africa
• Overseas Trust Bank, a defunct bank of Hong Kong
• OTB Group, a holding company for several fashion brands
• The Old Timer's Bulletin, an amateur radio history journal