B1 or B-1 may refer to:

• Vitamin B1.
• B1, a television station in Berlin, Germany.
• HMS B1, a B-class submarine of the Royal Navy.
• USS B-1, a B-class submarine of the United States Navy.
• The B-1 Lancer, a USAF heavy bomber aircraft.
• B1, an international standard paper size (1000×1414 mm), defined in ISO 216.