UID may refer to:
- Unique Identification Number later renamed as Aadhaar number, an initiative of Unique Identification Authority of India of the Indian government to create a unique ID for every Indian resident.
- UID = VAT identification number (in German language) (VAT: Value added tax)
- Ulster Institute for the Deaf
- Umeå Institute of Design
- Unitedworld Institute of Design, college in India
- Universal Instructional Design, an educational method that tries to deliver teaching to meet the needs of wide variety of learners.
- Unintelligent Design, a satirical reaction to the Intelligent Design movement
- Unique identifier
- PubMed 'Unique Identifier' parameter designating specific scientific publication abstracts; see: PMID
- 'Unique Item Identifier', a specific value in the Item Unique Identification system used by the United States Department of Defense for the identification of accountable equipment according to DoD Instruction 5000.64
- A nonprofit organization in Tokyo, Japan responsible for the Ucode system for uniquely identifying real-world objects electronically
- Unidentified decedent, a deceased person whose body has not yet been identified.