UIN may refer to:
Common User Identification Number, used by many computer security systems and ICQ, see ICQ#UIN, Unique identifier and User (computing) Universal Identification Number used for people, see National identification number and Unique Identification Authority of India, see also Permanent account number (PAN) used for inventory, see also UID University Identification Number, used by many universities for students, faculty and alumni Unit Identification Number, used by the military, see Military unit Unit Identification Number, used by the Department of Education, see Integrated Postsecondary Education Data System Unique Identification Number, similar to Universal Identification Number used for people and inventory, see above, and often replaced by Universally unique identifier (UUID)
Other uses User Intelligent Network, a type of network artificial intelligence, see, for example Personal communications network Airport code for Quincy Regional Airport in Illinois, United States