UDI may refer to:
- Unilateral declaration of independence, an assertion of the independence of an aspiring state or states
- In particular, the Rhodesian Unilateral Declaration of Independence
- Unidad de Inversion, Mexican currency funds unit
- Unión Demócrata Independiente, a political party in Chile
- Uniform Driver Interface, a project to develop portable device drivers
- Unified Display Interface, digital video interface specification based on DVI
- Universal Disk Image, a disk image format
- United Defense Industries, a major supplier of land warfare systems, now part of BAE Systems Land and Armaments
- United Diving Instructors, a diver training organization
- The SIL code for the Udi language
- Unknown Drunken Injury
- Unique Device Identification, a system that is intended to assign a unique identifier to medical devices within the United States
- Universal Design for Instruction or Universal Instructional Design