There is a growing need for timber-based solutions in construction, preferably in forms that are resistant to discolouring and degrading organisms. Discolouration, e.g., by stains and mould fungi, limits the performance of timber. Mould also has a drastic impact on indoor air quality and, thus, on the health of human beings. Furthermore, the aesthetic appearance of building components can be compromised by stains. Wood modification processes are industrial processes that result in wood-based materials that are non-toxic in service and, when disposed of at the end of their life, do not generate any toxic residues. As environmental concerns have grown significantly over several decades, interest in biobased solutions across various sectors of society has increased, and new modification processes and materials are continually being developed worldwide. This chapter presents modification methods applied to overcome the weaknesses in wood material that are primarily related to moisture sensitivity, low dimensional stability, low hardness and wear resistance, low resistance to biodeterioration caused by fungi, termites, or marine borers, and low resistance to UV irradiation.