MDN may refer to:
- Macedon railway station, Victoria, Australia
- Maiden Newton railway station, England; National Rail station code MDN
- Mark der Deutschen Notenbank; the official unit of currency in East Germany from 1964 to 1967
- Meriden (Amtrak station), Connecticut, United States; Amtrak station code MDN
- Message Disposition Notification, a form of return receipt for e-mail
- Ministério da Defesa Nacional, the Portuguese defence ministry.
- Mozilla Developer Network, a Mozilla website for developer documentation.
- Movimiento Demócratico Nicaragüense (Nicaraguan Democratic Movement).
- MdN Interactive, Macintosh designers Network magazine
- mobile device number, mobile dialable number, or mobile directory number