OPF may stand for:

• Miami-Opa Locka Executive Airport, Florida
• Orbiter Processing Facility, a hangar at Kennedy Space Center, Florida
• OEB Package Format, an eBook format
• OpenProject Foundation, the foundation for the open source web-based application OpenProject, registered 2012 in Berlin, Germany
• OpenProjectsFoundation, an open source software foundation, registered 2007 in Sofia, Bulgaria
• Optimal Power Flow, a technique used to simulate load flow through an AC power system

• Hard Ons
• Hardons
• Hard On The Levee (Frankie Miller song)
• Hard on the Outside, Soft in the Middle
• Hard on the Outside, Soft in the Middle (Popular episode)
• Hard out Here for a Pimp
• Har Dov
• Hard pack
• Hard Pan
• Hard Paste Porcelain
• Hard point
• Hard polytheism
• Hard Polytheism
• Hard problem
• Hard Problem of consciousness
• Hard punk core
• Hard Rain (band)
• Hard Rain Don't Last
• Hard Rain (Hard Rain album)
• Hard Rain (movie)
• Hardraw
• Hardraw Scar
• Hard realtime
• Hard real-time system
• Hard reset