As a natural and renewable polysaccharide, hemicellulose has been increasingly recognized as a promising biopolymer for developing sustainable and biodegradable ecomaterials. It offers a viable solution to pressing environmental challenges, such as plastic pollution and the depletion of fossil resources. In this review, we discuss the structural characteristics of hemicellulose, highlighting that its flexible structure and relatively higher reactivity compared to cellulose and lignin offer greater potential for chemical modification. Various extraction methods, including physical processes such as steam explosion and hydrothermal pretreatment, as well as chemical approaches like acid, alkali, or ionic liquid treatments, were reviewed along with their respective advantages and limitations. Hemicellulose can be processed into films, coatings, hydrogels, and aerogels, with excellent properties enhanced through cross-linking, polymer blending, and the incorporation of nanofillers. Potential applications include biodegradable food packaging with improved barrier and antioxidant capacity, water treatment through adsorption of dyes and metals, and biomedical uses including drug delivery, tissue engineering, and wound healing. Finally, we outline limitations, including challenges related to heterogeneity, mechanical strength, and scalability, while also highlighting future opportunities in chemical modification, composite development, and integration into circular bioeconomy models to replace petrochemical-based materials and advance environmental sustainability.