This chapter focuses on physicochemical and mechanical characterization of composites made from renewable materials. Most common renewable materials used in composites are natural fibers and polymers based on starch or vegetable oil. The extent of using renewable materials in biocomposites has increased during the past decade due to extensive research on cellulosic fibers and biobased polymers. Earlier, the research was focused on using the natural fibers as reinforcement in crude oil-based polymers such as polypropylene. Later, the emphasis shifted to increase the amount of renewable components in the biocomposites which led to the introduction of biobased resins in the composites. The properties of some biocomposites are today comparable to the properties for commercially available nonrenewable composites. Several plant biofibers have been used as reinforcement in biobased thermoplastics or thermosets to manufacture biocomposites. Material characterization is important to understand the performance of these composites under specific environment. Detailed discussion about the mechanical and physicochemical characterization is provided in this chapter. Physicochemical characterization includes chemical composition, density, viscosity, molecular weight, melting temperature, crystallinity, morphology, wettability, surface tension, water binding capacity, electrical conductivity, flammability, thermal stability, and swelling. Mechanical characterization includes tensile, flexural, impact, compressive, shear, toughness, hardness, brittleness, ductility, creep, fatigue, and dynamic mechanical analysis. © 2017 Scrivener Publishing LLC.