MD, Md, mD or md may refer to:
- Moldova (ISO country code MD)
- Maryland (United States postal abbreviation MD)
- Magdeburg (vehicle plate prefix MD), a city in Germany
- Mödling District (vehicle plate prefix MD), in Lower Austria, Austria
- Major Douglas (1879–1952), British Engineer and pioneer of the Social Credit economic reform movement
- Muhammad (name) or Mohammed (Md)
Music
- Main droite or mano destra (MD or m.d.), used in piano scores to mark sequences of notes that are to be played with the right hand
- MiniDisc, an optical storage medium developed by Sony
- Music director; the term "MD" is used particularly in musical theatre
- MDs (TV series), a 2002 made-for-television medical drama
- Materiali e discussioni per l'analisi dei testi classici, ("Materials and discussions for the analysis of classical texts"), an Italian classics journal
- Mega Drive, a game console produced by Sega
- Air Madagascar (IATA airline code MD)
- McDonnell Douglas (aircraft model prefix MD), a former aerospace manufacturer that later merged with Boeing
Biology and medicine
- Doctor of Medicine (MD), from the Latin Medicinae Doctor
- Medial dorsal nucleus, a large nucleus in the thalamus
- Muscular dystrophy, a genetic and hereditary muscle disease
- MD (Ayurveda), a degree in the Indian medical system of Ayurveda
Computing
- .md, Internet top-level domain for Moldova
- Markdown (file extension .md), a format
- mdadm (multiple device), a device driver used to support RAID in the Linux kernel
- Message-digest algorithm, a cryptographic hashing function
- Microdrive, a type of miniature hard drive
- mkdir or md, an operating system command to create a directory
Other uses in science and technology
- Mean absolute difference, a measure of statistical dispersion
- Mendelevium (Md), a chemical element
- Mesoscale discussion, a short-term technical meteorological forecast concerning convection; See Storm Prediction Center or Weather Prediction Center
- Methyldichloroarsine, a blister agent used in chemical warfare
- Millidarcy (mD), a unit of fluid permeability
- Molecular dynamics, a method of computer simulation of molecular interaction
- Membrane distillation, a process of membrane filtration
- Earthquake duration magnitude (Md )
- MD, 1500 in Roman numerals
- Majority decision, a winning criterion in several full-contact combat sports
- Man-day, amount of work performed by the average worker in one day
- Managing director, a chief executive
- Marque déposée (MD), an international trademarking symbol in countries where French is the dominant language; See Unicode subscripts and superscripts
- Match Director (MD), person who handles the overall match administration before, after and during an International Practical Shooting Confederation match
- Memorial Day