NDA is an abbreviation that may refer to:
- National Democratic Alliances
- National Democratic Alliance for Egypt
- National Democratic Alliance (India), a political coalition of India
- National Democratic Alliance (Georgia)
- National Democratic Alliance (Iraq)
- National Democratic Alliance (Israel) - a common misnomer for the National Democratic Assembly
- National Democratic Alliance (Italy) (defunct party)
- National Democratic Alliance (Kuwait)
- National Democratic Alliance (Malawi)
- National Democratic Alliance (Sierra Leone)
- National Democratic Alliance (Sudan)
- National Democratic Alliance (Trinidad & Tobago)
- Others
- National Dance Association, the oldest American organization for dance education
- National Defence Academy (India), a military academy in India
- National Defence Act, the primary enabling legislation for organizing and funding Canada's military
- National Defense Academy of Japan, a military academy in Japan
- National Democratic Assembly, the English name of the Israeli political party Balad
- National Dental Association, an association for African-American dentists.
- National Disability Authority, an agency of the Irish Department of Justice and Equality
- Net Daemons Associates, a computer network and systems administration company
- New Drug Application, the application needed to get a new drug approved in the United States by the Food and Drug Administration
- New Dynamics of Ageing, a multidisciplinary research initiative with the aim of improving quality of life of older people.
- Ninth Doctor Adventures - a series of books based on Doctor Who
- Nicolas Dupont-Aignan, a French politician
- Non-Destructive Analysis, a way to test, measure, or evaluate a material's properties without destroying it
- Non-disclosure agreement, a legal contract between at least two parties that outlines confidential material, knowledge, or information
- Northern Domestic Airspace, a Canadian aviation organization
- Nuclear Decommissioning Authority, an entity of the UK government