OMB is a three-letter abbreviation which may stand for:
- One-man band, a musician performing in two or more instruments at the same time, it is very common by buskers, mainly playing country, folk, and blues.
- Office of Management and Budget, a group that oversees the activities of federal agencies in the United States
- Owner Managed Business, small and medium enterprises
- Olympiade Mathématique Belge, the Belgian Mathematical Olympiad, a mathematical competition
- Ontario Municipal Board, a tribunal involved in municipal and planning matters in the province of Ontario, Canada
- Our Miss Brooks, an American situation comedy, starred Eve Arden
- Marine Modeling and Analysis Branch, formerly Ocean Modeling Branch, a US weather & environment agency
- Oregon Marching Band, the marching band for the University of Oregon in Eugene, Oregon, United States
- OpenMicroBlogging, the standard that allows for micro-blogging services to interoperate
- OMB, a graphic design studio founded by Oscar Mariné Brandi
- Organic Matter from Biomass, in Agriculture.