Cellulose-based hydrogels (CBHs) are three-dimensional polymeric networks derived from natural, nanostructured, or chemically modified cellulose, offering outstanding biocompatibility, biodegradability, and tunable physicochemical properties. Owing to their intrinsic hydrophilicity and structural versatility, CBHs have garnered increasing attention for the use in biomedical, tissue engineering, sensors, agricultural, and environmental applications. This chapter presents a comprehensive overview of the sources and types of cellulose, followed by detailed discussions on the synthesis strategies of CBHs, including physical, chemical, and radiation-induced cross-linking methods. Meanwhile, the fundamental properties of CBHs, including mechanical strength, swelling behavior, porosity, and biodegradability, are examined thoroughly. Emphasis is placed on how the synthesis parameters and structural design affect these properties and their implications for specific applications. This chapter aims to provide foundational knowledge and design insights for the development of advanced, sustainable hydrogel systems from cellulose-based materials.