MDO can mean:
- Multidisciplinary design optimization, a field of engineering
- Medium density overlay, a type of plywood
- MDO (band), a Puerto Rican boy band, a spin-off from Menudo
- Marine Diesel Oil, a type of fuel oil used in the maritime field
- Multi-decadal oscillation of ocean temperature, e.g. Atlantic multidecadal oscillation
- Mobile data offloading The practice of redirecting data from a cellular network to a fixed-line network
- Meritorious Day Off A day given off for meritorious military service