MDR or mdr may refer to:
- Masters in Dispute Resolution
- Mammalian diving reflex
- Mandar language
- Marina del Rey, California
- medical device reporting
- Metropolitan District Railway
- Merchant Discount Rate, the percentage of the transaction amount that the credit card processing company charges for providing the merchant the authorization to accept credit cards
- Michael David Rann, premier of South Australia
- Mitteldeutscher Rundfunk, the public broadcaster for the German Länder (States) of Thuringia, Saxony and Saxony-Anhalt
- Memory data register, a hardware register where data to be transferred to/from memory are temporarily stored
- M. D. Ramanathan, carnatic music artist
- "Mort de rire", French for die laughing equivalent to LOL in English
- Mouvement démocratique républicain, a former political party of Rwanda
- Multiple drug resistance, when a disease has evolved to become resistant from multiple drugs
- Multifactor dimensionality reduction, an algorithm for detecting interactions
- Mdr1, a plasma membrane protein, inside a living cell, able to pump out drug molecules. Unusually highly expressed in stem cells in order to protect the genome from mutagenic compounds
- Mini D ribbon, a cable connector type
- Major District Road