Much of the research on wood-plastic composites (WPC) has focused on formulation development and processing while high biological durability of the material was assumed. The gap between assumption and knowledge in biodeterioration of WPC needs to be reduced. Although some information on the short-term resistance of WPC against biological degradation is available, long-term data are required in order to adequately evaluate the performance of these relatively new materials and to enable use of WPC for structural applications. The influence of abiotic factors on material performance also has to be considered. Thus, further market growth and differentiation, especially in Europe, may be achieved while simultaneously standardization issues are dealt with.