FNN can mean:
- Financial News Network was a 1980s U.S. television channel. It was purchased in 1991 by CNBC, and subsequently ceased operations
- Flat Neighborhood Network, a type of computer network
- FNN algorithm (False Nearest Neighbors)
- Fuji News Network is a commercial television news network in Japan. The network is run by Fuji Television Network, Inc.
- Full National Number, in telecommunications, is the complete phone number for a line including the area codes