FEFLOW (Finite Element subsurface FLOW system) is a computer program for simulating groundwater flow, mass transfer and heat transfer in porous media. The program uses finite element analysis to solve the groundwater flow equation of both saturated and unsaturated conditions as well as mass and heat transport, including fluid density effects and chemical kinetics for multi-component reaction systems. The software was firstly introduced by Dr. Hans-Jörg G. Diersch in 1979. He developed the software in the Institute of Mechanics of the German Academy of Sciences Berlin up to 1990. In 1990 he was one of the founders of WASY GmbH of Berlin, Germany (the acronym WASY translates from German to Institute for Water Resources Planning and Systems Research), where FEFLOW has been developed further, continuously improved and extended as a commercial simulation package. In 2007 the shares of WASY GmbH were purchased by DHI Group. The company has since been renamed to DHI-WASY GmbH and FEFLOW became part of the DHI Group software portfolio.
The program is offered in both 32-bit and 64-bit versions for Linux and for Microsoft Windows operating systems. With version 6.0 in 2010 a newly developed user interface based on the framework Qt has been introduced.
Prior versions and the so-called FEFLOW 6.0 Classic interface are based on the Motif widget toolkit, using a proprietary X Window System, Hummingbird Exceed on Microsoft Windows operating systems. Support for UNIX platforms ended with version 5.3; prior support was provided for IRIX, Tru64, and Solaris.