A9

A9, A.9, A09, A 9 or A-9 may refer to

Science

 * ATC code A09 Digestives, including enzymes, a subgroup of the Anatomical Therapeutic Chemical Classification System
 * Biolimus A9, an immunosuppressant
 * British NVC community A9, the Potamogeton natans community, one of the aquatic communities of the British National Vegetation Classification
 * HLA-A9, a broad antigen serogroup of Human MHC HLA-A
 * Subfamily A9, a Rhodopsin-like receptors subfamily

Technology

 * A9home, a small form factor computer
 * A9.com, a website and search engine by Amazon.com
 * Apple A9, a 64-bit system on a chip (SoC) designed by Apple Inc.
 * Hanlin eReader A9, an ebook reader

Aviation

 * Breda A.9, a 1928 Italian biplane trainer aircraft
 * CallAir A-9 Quail, an agricultural aircraft
 * Georgian Airways's IATA code
 * Lockheed A-9, a ground attack aircraft based on the Lockheed YP-24 fighter prototype
 * Northrop YA-9, a ground-attack aircraft that competed with the Fairchild Republic A-10 Thunderbolt II

Military

 * A9, a military staff designation in the continental staff system
 * A 9, a Swedish artillery regiment
 * A9, a model of German Aggregate Series Rocket from World War II
 * Cruiser Mk I (A9), a British tank

Music

 * A9 (band), a Japanese rock band originally named Alice Nine
 * A-9, a Gibson mandolin guitar model

Other uses

 * A9 (classification), an amputee sport classification
 * A9 road, in several countries, see List of A9 roads
 * A9, an international ISO 216 paper size standard (37×52 mm)
 * A-9 Vigilance, a fictional starfighter from the Star Wars universe
 * Arrows A9, a 1986 British racing car
 * HMNZS Manawanui (A09), a 1988 diving support vessel for the Royal New Zealand Navy
 * HMS A9, an A-class submarine of the Royal Navy
 * Réti Opening or A09, a chess opening
 * A9 TV, a Turkish television station