Cellulosic biorefinery, utilizing industrially important proteins like cellulases, holds promise for a zero-waste, sustainable future. However, high production costs and low yields hinder commercialization. On-site production strategies and genetic engineering have been employed to improve cellulase production. This review delves into cellulase structure, production methods, optimization, and factors affecting production. It also highlights genetic engineering approaches like heterologous expression, RNA interference, and CRISPR-Cas9 for enhancing cellulase production. The applications, limitations, and prospects in various biotechnological sectors are discussed, offering insights into a zero-waste cellulosic biorefinery future.