DD, dd, or other variants may refer to:
- DD in hexadecimal = 221
- DD, a brassiere measurement
- Companies
- d.d., Croatian term for a public limited liability company; dioničko društvo (literal: joint stock company)
- DD National or DD1, an Indian national channel
- DuPont's stock ticker symbol
- Computing
- .dd, a hypothetical domain name for the German Democratic Republic
dd, an HTML element for specifying definition data- dd (Unix), a program that copies and convert files and data
- Deckadance, a DJ program for Windows and Mac OS X designed by Image-Line
- Deployment descriptor, a component in Java Platform, Enterprise Edition applications
- Logo for Dolby Digital, audio compression technologies developed by Dolby Laboratories
- Double density, a capacity designation on magnetic storage, usually floppy disks
- Entertainment
- Daredevil, a Marvel Comics character
- DD, a character in The Saga of Seven Suns novels by Kevin J. Anderson.
- Military
- DD tank, an amphibious tank
- Dishonorable discharge, a punitive discharge in the US Military
- DD, the US Navy hull classification for destroyers
- Science and technology
- Data Deficient, a rating on the IUCN Red List of Threatened Species
- Decimal degrees, geographic coordinates shown using decimal fractions
- Transportation
- D-D locomotive, the AAR classification for a railway locomotive with two four-axle bogies
- Nok Air's IATA code
- DD, the licence plate code for Dresden, Germany
- Other uses
- Dd (digraph), a digraph in the Welsh language
- Degree of Difficulty, a diving score modifier
- Doctor of Divinity or D.D.
- Direct deposit, used in banking
- Drug and Disease, used in Personals ads as "D&D Free"