Biotechnology of microalgae has gained importance in recent years due to the development of new production and environmental technologies. Because their growth requires unexpensive substrates such as solar light and CO,, microalgae can be used as cheap and effective biocatalysts to obtain high added-value compounds, from simple metabolites to complex molecules, i.e., chemicals, vitamins, carotenoids, pigments, or polysaccharides. During productive processes, the algal biomass formed may be used as a food source like proteins. On the other hand, microalgae can also be employed in contaminant bioelimination processes especially for nitrogen, phosphorus, or sulfur compounds. Particularly relevant is their use for heavy metal removal from wastewaters; upon enriching the biomass in the metal, they can be recovered, thereby providing economic advantages. The use of immobilized microalgae in these processes is very adequate and offers significant advantages in bioreactors.