FMI (Functional Mock-up Interface) is a standard for exchanging models between different modeling and simulation environments. FMI defines a model execution interface consisting of a set of C-function signatures for handling the communication between the model and a simulation environment. Models are presented as ODEs with time, state and step events. FMI also specifies that all information related to a model, except the equations, should be stored in an XML formated text-file. The format is specified in the standard and specifically contains information about the variables, names, identifiers, types and start attributes.

A model is distributed in a zip-file with the extension '.fmu', containing several files. These zip-files containing the models are called FMUs (Functional Mock-up Units). The important files in an FMU are mainly the XML-file, which contains the definitions of all variables and then files containing the C-functions which can be provided in source and/or binary form. FMI standard also supports providing documentation and resources together with the FMU. For more information regarding the FMI standard, please visit http://www.functional-mockup-interface.org/.