Cin, CIn or CIN can mean:
- The Cincinnati Reds, an MLB franchise.
- The Cincinnati Bengals, an NFL franchise.
- The Amtrak code for Cincinnati Union Terminal
- Cervical intraepithelial neoplasia
- Chromosome instability
- The ICAO-code of Constellation Airlines, a defunct Belgian airline
- Corporação Industrial do Norte, Portuguese-owned company that is the Iberian market leader for paint & coating products
- Convective inhibition
- Contrast-induced nephropathy
- An object of the C++ Iostream header file (C-In).
- Card Identification Number
- Children in Need, an annual UK Telethon Fundraiser shown on the BBC
- Cineon file format (filename extension ".cin")
- corporate identification number or corporate identity number – for corporations in India
- Cosine integral (standard mathematical symbol "Cin")
- The Crime & Investigation Network
- The Caribbean International Network (CIN TV)
- The Carmel Infortainment Network (CIN in a secondary school of Hong Kong)
- Kadir Cin, Turkish volleyball player