N3 may refer to:

• N3 (Bangladesh), connecting Dhaka and Mymensingh
• N3 road (Belgium), one of the national roads in Belgium
• National Road 3 (Democratic Republic of the Congo)
• N3 road (Gabon)
• N3 road (Ghana)
• N3 road (Ireland), a National Primary Route
• N3 motorway (Netherlands), one of the national roads in the Netherlands
• N3 road (Senegal), one of the national roads in Senegal
• N3 (South Africa), a road connecting Johannesburg to Durban
• Route nationale 3, France

• N3-class battleship, a Royal Navy battleship design that was never built
• USS N-3 (SS-55), a 1915 coastal defense submarine of the US Navy
• SP&S Class N-3, a steam locomotives class from the Spokane, Portland and Seattle Locomotive Roster
• N₃, gauges for monitoring a third section in a triple spool jet engine
• N3, IATA code for the Russian airline Omskavia
• N3, European large goods vehicles above 12 tonnes
• N3 Pup - the Preceptor N3 Pup ultralight aircraft (and derivatives)

• Haplogroup N (Y-DNA), a former human Y-chromosomal haplogroup, now N1c
• n-3, Omega-3 fatty acid
• Trinitrogen (N₃), inorganic molecule composed of three nitrogen atoms
• N−3, an azide anion in chemistry
• N³⁻, a nitride anion in chemistry
• N3 Lung cancer, metastasis to certain lymph nodes
• N₃, the genus three non orientable surface
• N3, cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II), a red dye in dye-sensitized solar cells
• N3, abbreviation for the 3 nanometer process node in semiconductor technology

• N3 (Calgary), condominium building
• N3 (NHS), the national broadband network for the English National Health Service
• Notation3, or N3 rules, a textual notation for the Resource Description Framework
• N3, the third level of the Japanese-Language Proficiency Test
• N3, the most recent version of the Nagravision conditional access system for cable and satellite television
• N3, a postcode district in the N postcode area in London
• N3, the former name of NDR Fernsehen, a German television channel

• N03, the ICD-10 code for Nephritic syndrome
• ATC code N03, Antiepileptics, a subgroup of the Anatomical Therapeutic Chemical Classification System
• 3N (disambiguation)
• List of highways numbered 3
• N road (disambiguation)