Abstract: We present a simple and generic algorithm for interactive ray tracing of free-form surfaces, allowing for a simple implementation for bicubic Bézier surfaces. The algorithm uses a fixed number of on-the-fly refinement steps to prevent crack appearance. Furthermore, we show that grouping rays into coherent bundles and tracing them together achieves a speed-up factor of more than 5 compared to tracing only single rays. Combining ray-bundle-based ray tracing with optimized kd-tree construction even allows for interactively ray tracing completely dynamic scenes with thousands of patches. Even highly complex scenes consisting of a million Bézier patches can be interactively ray traced while requiring only a few seconds startup time. Source code is available online.