This contribution deals with the data processing system for our scanning tunneling microscope (STM). Since several collaborators should have access to our STM data, we have decided to separate between data acquisition and data processing. The data acquisition system based on a cheap 8-bit microcomputer controls all aspects of the scanning process, stores the data on disk, and transmits them to the data processing system. Image processing and computer graphics have become more important in scanning tunneling microscopy. We use two μVAX II’s which are connected by a network, one as a storage device (527-MByte disk), the other as a graphic processor (256 colors). We have developed a highly interactive software package which allows manipulating and displaying the STM data. This package includes utilities to fit a plane or a hyperbolic paraboloid and subtract it from the image. The line plots of topography and the local barrier height can be viewed from different point of view. Top-view images can be displayed both in color with different color lookup tables, which can be chosen interactively, and in gray scale. The images can be displayed at higher resolution by a bilinear interpolation. Light sources illuminate the surface to get flat and Gouraud shading. The shading can be combined with perspective or parallel projection and hidden surface removal. There is also a fast Fourier transformation algorithm and a utility for interactive digital filter design implemented. There are utilities to create stereoscopic pictures. Significant examples of the application to images of graphite and of nanometer scale structure images are presented.