MDN may refer to:

Computing and technology

• MDN Web Docs (formerly Mozilla Developer Network), a Mozilla website for developer documentation
• Message Disposition Notification, a form of return receipt for e-mail
• Telephone number for mobile devices, as in:
  • Mobile device number
  • Mobile dialable number
  • Mobile directory number

Organizations

• Ministry of National Defence (Portugal) (Ministério da Defesa Nacional), the Portuguese defence ministry
• Nicaraguan Democratic Movement (Movimiento Demócratico Nicaragüense)

Transport

• Macedon railway station, Victoria, Australia (station code: MDN)
• Madison Municipal Airport (Indiana), Madison, Indiana, United States (IATA code: MDN)
• Maiden Newton railway station, England (National Rail station code: MDN)
• Medan railway station, North Sumatra, Indonesia (station code: MDN)
• Meriden (Amtrak station), Connecticut, United States (Amtrak station code: MDN)
• Minggang East railway station, China (China Railway telegraph code: MDN)
• Morden tube station (London Underground station code: MDN)
• Mudan Airlines, Somali Republic (ICAO code: MDN)

Other uses

• East German mark (Mark der Deutschen Notenbank), the official unit of currency in East Germany from 1964 to 1967
• Maya Day Number, the sum of days in Mesoamerican Long Count calendar
• Mbati language (ISO 639-3: mdn)
• MdN Interactive, the magazine for Macintosh designers Network
• MDN, a television station in Griffith, New South Wales, and sister station of MTN