Man Machine Interface (MMI) is a software application (typically a using Graphical User Interface or GUI) that present information to the operator about the state of a process, and to accept and implement the operators control instructions. It may also interpret the plant information and guide the interaction of the operator with the system. A MMI is often a part of a SCADA (Supervisory Control and Data Acquisition) system; nevertheless, the terms are often used synonymously.

MMI products include Iconics Genesis (www.iconics.com), InduSoft WebStudio (www.indusoft.com), Proficy iFIX (www.gefanuc.com), and Wonderware (www.wonderware.com).

An MMI is also known as a Human Machine Interface (HMI).