A composite is a material consisting of two or more materials permanently bonded together at a microscopic or macroscopic level to create a new material that, in its entirety, has properties that differ from those of the basic materials. The properties of polymer blends also differ significantly from the properties of the polymer materials that were used for the blend. Just as there are now countless different plastics with a wide variety of properties, there are also endless possibilities for producing blends and composites. They all aim to create a new, even better material by combining different materials. These composites and blends are usually precisely tailored and optimized for a specific application. Against the background of sustainable raw material management, materials based on renewable raw materials are of great interest for composites and blends, as they can reduce the carbon footprint. Regenerated cellulose fiber-reinforced plastics (RCF), for example, show some advantages over glass fiber-reinforced plastics (GF), especially regarding the high elongations that these fibers made from renewable raw materials can absorb. In the field of blends, too, new material combinations and thus new areas of application can be developed not only by combining different bio-based plastics but also by using renewable raw materials such as starch and lignin as blend partners. Natural fibers and wood also offer a wide range of possible applications for composites, including the use as filler and reinforcing fibers in natural fiber composites (NFC) or wood-plastic composites (WPC) and as wood veneer or plywood in combination with other materials in large-area composites. The following pages therefore present and put into context some composites and blends that are fully or at least partially bio-based and whose properties have been tailored to various specific applications.