The creation of materials exploiting molecules from renewable resources and green processing routes in order to minimize contamination of the environment with toxic solvents and starting components, is an important step towards a sustainable society, and sustainable development is critical in all technological fields including biomedical engineering. In this context, the polysaccharides are an important family of molecules, as they can be derived from numerous natural sources including plants, bacteria, insects, animals, and also from by-products/waste-materials obtained from agricultural or fishery activities. Also, polysaccharides are biodegradable and can be broken down by common microorganisms found on land or in water. In nature, polysaccharides can be composed of one type of repeating unit (homopolysaccharides; starch and cellulose) or two or more types of repeating monomer (heteropolysaccharides; pectin, alginate). But despite using only a few basic building blocks, many unique and complex molecular structures with specific features and functions are assembled giving rise to a plethora of diverse carbohydrates. Some of the polysaccharides are classified as polyelectrolytes, and these are either negatively or positively charged. The intrinsic properties of such ionic polysaccharides are used in material science to produce stimuli-responsive materials where external stimuli (pH, ionic strength, and temperature) trigger, for example, a mechanical response in the material or a swelling mechanism that can be exploited in drug delivery. In addition to conventional polysaccharides, advanced genetic engineering also opens up the possibility for new, innovative, and structurally designed macromolecules with specific chemical and physical properties, allowing for better material structure-property control. Natural polysaccharides are typically biocompatible, possibly bioadhesive, and generally recognized as safe (GRAS) and, in conclusion, they are attractive materials to use in biomedical applications.