B9, B IX or B-9 may refer to:

Science

• Prodelphinidin B9, a plant phenolic compound
• Vitamin B₉, another name for folic acid
• B-Nine WSG, a formulation of the plant growth regulator daminozide
• Boron-9 (B-9 or ⁹B), an isotope of boron
• A subclass of B-class stars

Transport

• B9 (Croatia), a road part of the Istrian Y highway complex
• B9 (New York City bus) serving Brooklyn
• Bundesstraße 9, a federal highway in Germany
• Iran Airtour (IATA code B9)
• Air Bangladesh (former IATA code B9)

Vehicles

• Bavarian B IX, an 1874 German steam locomotive model
• Bavarian B IX (Ostbahn), an 1869 German steam locomotive model
• Bensen B-9, a 1958 American small helicopter
• Boeing B-9 (sometimes referred to as the Y1B-9 or YB-9), a 1931 United States Army Air Corps bomber
• HMS B9, a British Royal Navy B-class submarine
• LNER Class B9, a class of British steam locomotives
• The former model name for the Subaru Tribeca

Organizations

• The abbreviation used for the record label Bridge Nine
• Bucharest Nine (B9), a group of nine NATO members: Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia

Other uses

• Iceberg B-9, a 1987 iceberg calved away from Antarctica
• Model B-9 on the TV series Lost in Space, otherwise known simply as “Robot (Lost in Space)“
• An international standard paper size (44×62 mm), defined in ISO 216

See also

• 9B (disambiguation)