Universal file format developed by Electronic Arts; may contain text, image, or audio data; used as the basis for several other file formats and is supported by many programs.

IFF files are made up of sections of data called "chunks" that are defined with four-letter IDs; the three main chunk types are FORM, LIST, and CAT; FORM specifies the format of the file, LIST includes the properties of the file, at CAT includes the rest of the data; each chunk may contain text, numerical data, or raw data.

IFF files used by The Sims and The Sims Online can be edited using IFF Pencil for Windows or IFF Snooper for the Mac.