IID may refer to: Interface Identifier, the last 64-bits of an IPv6 address Internet identity, a social identity used by Internet users Internet Identity, an Internet security company Ignition interlock device, a breathalyzer connected to a vehicle's engine Independent and identically distributed random variables in probability theory Interaural intensity difference in determining the location of a sound Internal Investigations Division (in law enforcement) IRIX Interactive Desktop, software for interacting with a computer running the IRIX operating system Iterative and Incremental Development in software development A COM Interface ID Invoke Image Display an Integrating the Healthcare Enterprise (IHE) Integration Profile Imperial Irrigation District IID (Imperial Institute of Design), a design school in Monteswar, West Bengal, India See also 2D (disambiguation), including a list of topics named II-D, etc.