Cellulose-based aerogels (CBAs) have emerged as highly versatile materials for environmental remediation and catalysis, thanks to their unique combination of high porosity, low density, biodegradability, and tunable surface functionality. This chapter provides a comprehensive overview of the latest advancements in the synthesis, modification, and application of CBAs in these fields. The focus is on their performance in key areas such as heavy metal ion adsorption, organic pollutant removal, oil–water separation, gas adsorption and separation, photocatalytic degradation, and catalytic organic transformations. The inherent hydroxyl-rich surface and three-dimensional network architecture of CBAs offer abundant active sites and enhance mass transport, making them ideal for both adsorption and catalysis. Additionally, CBAs have shown strong potential in enzyme immobilization and biocatalysis due to their structural compatibility and chemical modifiability. Continued innovations in material engineering and sustainable chemistry are expected to solidify CBAs as crucial components in next-generation environmental and catalytic technologies.