Hydrogels with very interesting properties such as high water content, porosity, swelling, and mimicking the structure of the extracellular matrix (ECM) are promising candidates for a variety of applications. Recently, great efforts are being made to improve the shape and functionality of three-dimensional (3D) hydrogels. One of the most promising approaches is the incorporation of metal or metal nanoparticles (NPs) into hydrogels made of natural and synthetic polymers such as proteins, carbohydrates (i.e. chitosan, carboxymethyl cellulose, hyaluronic acid, etc), and the development of dynamic functional hydrogels that have been extensively studied. This review article focuses on the incorporation of metals or metal NPs into hydrogels to enhance their functionality and properties. In the first part, various metal-based hydrogels including metal- coordinated hydrogels, metal-nanocomposite hydrogels, and their synthesis methods are discussed. Subsequently, various properties of metal-containing hydrogels such as mechanical, self-healing, bioadhesion, antibacterial activity, and conductivity are explained. Finally, stimuli-responsive metal-based hydrogels are discussed with a special focus on carbohydrate polymers. This review article presents a new perspective on the development of hydrogels for various biomedical applications.