This chapter describes rendering techniques and implementation considerations when using ray tracing for interactive scientific and technical visualization. Ray tracing offers a convenient framework for building high-fidelity rendering engines that can directly generate publication-quality images for scientific manuscripts while also providing high interactivity in a what-you-see-is-what-you-get rendering experience. The combination of interactivity with sophisticated rendering enables scientists who are typically not experts in computer graphics or rendering technologies to be able to immediately apply advanced rendering features in their daily work. This chapter summarizes techniques and practical approaches learned from applying ray tracing techniques to scientific visualization, and molecular visualization in particular. 27.1 INTRODUCTION Scientific and technical visualizations are used to illustrate complex data, concepts, and physical phenomena to aid in the development of hypotheses, discover design problems, facilitate collaboration, and inform decision making. The scenes that arise in such visualizations incorporate graphical representations of the details of key structures and mechanisms and their relationships, or the dynamics of complex processes under study. High-quality ray tracing techniques have been of great use in the creation of visualizations that elucidate complex scenes. Interactivity is a powerful aid to the effectiveness of scientific visualization because it allows the visualization user to rapidly explore and manipulate data, models, and graphical representations to obtain insights and to help confirm or deny hypotheses.