Some bacteria produce enzymes capable of breaking down cellulose, one of the main components of plant cell walls and a major constituent of agricultural waste, such as straw, crop residues, leaves, and stems. Cellulases play an important role in the decomposition of plant materials and the return of carbon to the ecological cycle. They are also valuable in agricultural and industrial applications. Cellulose consists of long chains of glucose units linked by chemical bonds that require specialized enzymes for their breakdown. The degradation system typically involves several enzymes that work together, including endoglucanase, which cleaves bonds within the cellulose chain; cellobiohydrolase, which releases cellobiose units or short fragments from the ends of the chains; and β-glucosidase, which converts certain intermediate products into glucose. Various bacterial species produce these enzymes, and their efficiency may vary depending on the structure of the cellulose and the surrounding conditions. The decomposition of plant residues does not depend on enzymes alone, as other components, such as lignin, can affect how easily cellulose can be accessed. Moisture, temperature, pH, and nutrient availability also influence the activity of microbial communities. In soil, cellulose-degrading bacteria work alongside fungi and other organisms to break down plant residues and recycle nutrients into the ecosystem. In industrial applications, cellulolytic enzymes can be used in the pretreatment of agricultural waste to produce sugars that may be utilized in fermentation processes for biofuel production or the manufacture of other compounds. Researchers are also investigating ways to improve the production of these enzymes by using suitable bacterial strains or optimizing fermentation conditions to increase efficiency and reduce costs. However, the effective utilization of agricultural waste requires consideration of the nature of the raw material, processing methods, and the intended final product. This process demonstrates how bacterial enzymes contribute to carbon cycling and transform plant waste into useful resources, supporting the development of biotechnological applications that promote the sustainable management of agricultural waste. Al-Mustaqbal University – The First University in Iraq