Most of the aquatic systems of tropical & sub tropical countries are infested with weeds, mainly Water Hyacinth (Eichhornia crassipes). Since all efforts to eradicate the weed have failed, the concept of "eradication through utilization" has gained importance, worldwide. We have focused on devising suitable strategies for the utilization of these weeds. In this book, our work on the development of a novel solid state fermentation technology for using water hyacinth biomass as substrate for production of industrial enzyme, cellulase, is presented. Three bacteria associated with aquatic weeds have been isolated, identified & used to produce cellulase enzyme using hyacinth as substrate under SSF. Various process parameters influencing enzyme yield have been optimized & a lab scale SSF system has been developed. Scale-up experiments using trays & SSF under non-sterile conditions has been tried. Enzyme produced was partially purified & characterized. Results are highly encouraging for the development of similar technologies for managing such weeds in other countries as well. The impact of weeds will be reduced & local level employment generated if such technologies are adopted.