NDI can refer to:
- Ndi is an Annang / Ibibio / Efik word that means "I am"
- National Democratic Institute for International Affairs
- National Datacast Incorporated, the PBS datacasting subsidiary
- Non-Destructive Inspection (see Nondestructive testing)
- Non-Developmental Item, in the Federal Acquisition Regulations
- National Dance Institute, a not for profit organization
- Nephrogenic diabetes insipidus, is a form of diabetes insipidus due primarily to pathology of the kidney.