A broad range of modalities for medical imaging has evolved over the last few decades. Even though the image quality improves steadily, just evaluating the plain image data visually is frequently insufficient for diagnosis or planning and supervising an intervention. Furthermore, automated methods were developed to extract essential data and parameters from the images, or to combine data from multiple sources, that require an adequate presentation. Aside from quantititative analysis, visualization of the original and derived data is therefore of paramount importance. This short course presents a tutorial in visualization techniques using the Virtual Reality Modeling Language (VRML), which is a text-based 3-D description language, and the Visualization Toolkit (VTK), an open-source software system. The tutorial consists of demonstrations and examples for the basics of modeling, animation, and interaction in either technique, and will show their advantages and limitations in medical applications.