B18 or B-18 may refer to:

• Alton Bay Seaplane Base (FAA LID: B18)
• B-18 Bolo, an American bomber aircraft by Douglas based on the Douglas DC-2
• B 18, a Swedish bomber aircraft made by SAAB
• B18 (New York City bus) serving Brooklyn
• B18 road (Cyprus)
• Caro-Kann Defence, in chess (Encyclopaedia of Chess Openings code B18)
• HLA-B18, an HLA-B serotype
• Honda B engine
• Volvo B18 engine
• Boron-18 (B-18 or ¹⁸B), an isotope of boron
• LNER Class B18, classified B1 until 1943
• 18th Street gang (Barrio 18)