Learn how NVIDIA's Material Definition Language (MDL) provides a consistent means to define material appearances for use in physically-based rendering with a highly flexible, layered approach. This presentation introduces the key ideas of MDL and how they address the challenge of matching looks between different renderers with a common definition - be they path tracers, basic ray tracers, or conventional rasterizers. Developers will learn how to transition from conventional shading languages to MDL while Material Authors and Artists will see through high quality examples how they can easily create and assign custom looks. The Iray 2013 rendering platform will be used to interactively demonstrate the use of MDL between multiple rendering modes and rendering techniques. The future of MDL, including support for Measured Materials from measurement devices will also be discussed.