Irish Free State, a state in Ireland which existed in the early part of the 20th century

Interference (intensity) fluctuation spectroscopy, related to dynamic light scattering, see Scattering

Internet File System, an Oracle java-based File System

Indian Foreign Service

Indian Forest Service

Installable File System, a filesystem API in IBM OS/2 and Microsoft Windows NT.

Institute for Fiscal Studies

Iterated function system a method of constructing fractals in mathematics and computer science

Industrial and Financial Systems - IFS AB, a Swedish company and author of ERP software

Independent Front Suspension, an early type of front-end independent suspension on many passenger vehicles

Initial Flight Screening, flight screening used as a prerequisite for Air Force Flight School

Ifs, Calvados, a commune of the département of Calvados, in the Basse-Normandie région, in France

International Financial Statistics, a database maintained by the IMF

Internal Field Separator, a special set of characters in Unix shells

Internal family systems, a school of psychotherapy, see Internal Family Systems Model

Integrated File System - on IBM midrange & mainframe systems (e.g. OS/400, MVS, VM/CMS), the POSIX compatible filesystem provided by the operating system, as opposed to the traditional non-POSIX filesystem it also supplies