to alleviate our reliance on petroleum-based materials. Beyond abundance and biodegradability, wood is also a carbon-neutral material that does not contribute net CO 2 increase due to the cyclic carbon fixation during photosynthesis and release during degradation. Given these advantages, wood has been considered as a potential replacement for petroleum-based materials to support continued sustainable growth.Throughout history, wood has been the primary material for tools, buil dings, and fuels that support human activity. However, the functions of wood have been limited by its intrinsic properties including bulkiness, low mechanical properties, nontransparency, and nonconductivity. Therefore, it has been gradually replaced by other materials, such as synthetic polymers, glass, and metals. With the advancement of nanotechnology, nanomaterials derived from wood have been successfully synthesized and are well suited to expand its application to more emerging areas such as the environment, energy, and biomedicine. Therefore, given the rapid expansion of bio-based nanotechnologies and the stringent demands for sustainable development, it is pressing to revisit wood-based materials as sustainable sources to satisfy our continuous needs, alleviating our fear of the depletion of nonrenewable natural resources.Here, we cover the most recent advances in designing hierarchical structures using wood and wood-based nanomaterials, including both the bottom-up assembly from nanocellulose into varied 1D, 2D, and 3D forms and the recently developed top-down approaches that introduce novel functionalities to existing wood hierarchical structures. Progress in the application of these hierarchical structures to emerging sustainable areas will be reviewed to emphasize how these traditional woody materials, now transformed by nanotechnologies, may be used to improve the sustainability of biodegradable flexible electronics, natural energy harvesting, thermal regulation in green buildings, sustainable energy storage, environmental remediation, and efficient solar steam generation toward desalination. To date, several very important reviews on the structures and applications of wood-and cellulose-based materials have been published, and due to the limited space available here, inclusion of comprehensive knowledge on all these aspects is infeasible. For more detailed reviews on each aspect, the readers will be directed to other more comprehensive or specific reviews. [1][2][3][4][5][6][7] The primary focus here will be placed on how these bio-based materials could potentially With over 30% global land coverage, the forest is one of nature's most generous gifts to human beings, providing shelters and materials for all living beings. Apart from being sustainable, renewable, and biodegradable, wood and its derivative materials are also extremely fascinating from a materials aspect, with numerous advantages including porous and hierarchical structure, excellent mechanical performance, and versatile chemistry. Here, strategies for designing n...