Wood is used to produce many products (structural and nonstructural) for applications in which its natural properties are adequate. With the decrease of wood availability and the increase of less durable, younger and faster-growing trees, it is possible to modify wood in various ways to improve the properties, depending on the ultimate application. Wood- polymer composites (WPCs) can be any combination of wood and polymer, from polymer filled with wood fiber to solid pieces of wood filled with polymer. This chapter refers to WPCs made from solid wood such as small pieces of wood or veneer. When wood and polymer are combined, the physical properties, surface hardness, water repellency, dimensional stability, abrasion resistance, and fire resistance can be improved over those of the original wood.