Advantage and application of high solid and Multi-phase Bioprocess Engineering startsdiscussion from very beginning and extends the discussions to a greater detail makingthis piece of work suitable for beginners as well as experts in this field. Multiple methodslike hydrolysis, Laboratory-scale method for enzymatic saccharification, model-basedoptimization, a statistical approach are described in a structured manner. In later part ofthe text, solid state fermentation has been explained considering Solid fermentation ofwheat bran for hydrolytic enzymes production and cellulase production. Also, scale upof Polygalacturonase Production by Solid State Fermentation Process along with consideringit as a Novel Paradigm for Organic Waste Valorization are discussed.