Polysaccharides display most of the properties needed for applications in catalysis, adsorption or remediation. Requisites common to these applications are appropriate surface functions to ensure substrate-material interactions, accessibility of the functional groups, and proper shaping for easy manipulation. Natural polysaccharides are well known as supports for enzymatic catalysts and gelling agents in aqueous phase, due to the high level of dispersion of hydrocolloids. However, they suffer from diffusional limitations in the dry state, due to the low surface area of the dried materials generally used, xerogels or lyophilized solids. This chapter deals with the proper methods to prepare dry materials which retain the dispersion of the polymer hydrogel, namely polysaccharide aerogels. The materials whose properties are described here are stable in most organic solvents and present numerous and diverse surface functionalities (like hydroxy, carboxy, or amino groups). Shaping and appropriate drying of gelling polysaccharides provide a new opportunity to obtain materials from one of the less energy-intensive sources of biomass. Their application in catalysis and adsorption could open substantial markets for products of seaweed harvesting and coproducts of the seafood industry.