The main operating system used for image processing in ESO is UNIX. On the SUN workstation the X11 OSF/Motif window system is used to provide virtual terminals or displays. For those who are not familiar with UNIX systems this section tries to provide a very basic introduction. For more information, the interested user is referred to the various UNIX or SUN publications. A few copies of these manuals and other documentation are available through system management (room 220/2).