ImageVis3D is a new volume rendering program developed by the NIH/NIGMS Center for Integrative Biomedical Computing (CIBC). The main design goals of ImageVis3D are: simplicity, scalability, and interactivity. Simplicity is achieved with a new user interface that gives an unprecedented level of flexibility. Scalability and interactivity mean that users can interactively explore terabyte-sized data sets on hardware ranging from mobile devices to high-end graphics workstations. Finally, the open source nature as well as the strict component-by-component design allow developers not only to extend ImageVis3D itself but also reuse parts of it, such as the rendering core. This rendering core for instance is planned to replace the volume rendering subsystems in many applications at the SCI Institute and with our collaborators.