Cellulose-based aerogels (CBAs) represent a sustainable class of materials with ultra-low density, high surface area, and exceptional porosity, offering significant potential for diverse applications including thermal insulation, environmental remediation, and energy storage. This chapter comprehensively examines the preparation pathways and resultant properties of CBAs derived from various cellulose sources (plant biomass, bacterial cellulose, and nanocellulose). It details the critical processing stages, which include raw material selection and pretreatment (delignification, nanocellulose production, dissolution), dissolution/dispersion in solvent systems (ionic liquids, alkali/urea, nanocellulose suspensions), gelation via physical (hydrogen bonding, freeze–thaw) or chemical crosslinking, and drying (freeze-drying, supercritical drying). The synthesis-structure–property relationships are emphasized, highlighting how processing choices impact the final aerogel's porosity, morphology, mechanical integrity, and functionality. Furthermore, the fabrication of specialized dimensional forms—films/membranes, continuous fibers (via wet spinning, freeze-spinning), and microspheres (via emulsification or simple dropping methods) is explored, demonstrating their application-specific advantages and tailored production routes. By integrating fundamental material science with process engineering, this chapter provides a foundation for designing high-performance, sustainable CBAs for advanced technological solutions.