ImageVis3D is a new volume rendering program. The main design goals of ImageVis3D are: simplicity, scalability, and interactivity. Simplicity is achieved with a new user interface. Scalability and interactivity for ImageVis3D mean that both on a notebook computer as well as on a high end graphics workstation, the user can interactively explore terabyte sized data sets. The open source nature and component-by-component design allow developers to extend ImageVis3D itself but also reuse parts of it, such as the rendering core.