We investigated the adhesion behavior of nanocomposite hydrogels (NC gels), consisting of unique organic (polymer)-inorganic (clay) network structures, toward inorganic and organic materials. The NC gels exhibit instant and strong adhesion to inorganic and organic substrates with hydrophilic porous surfaces. The NC gels instantly adhere to hydrophilic porous substrates (e.g., unglazed ceramic surfaces and polymer membranes) through simple light contact. In addition, a small piece of NC gel effectively joined two substrate samples (e.g., concrete blocks and bricks) through lamination of the interposing NC gel. The resulting conjoined materials were unable to be separated at the gel-substrate interface; rather, the gel itself fractured upon separation, which indicates that the adhesive strength at the interface is greater than the tensile strength of the NC gel. With the exception of NC gels with very high clay concentrations ( Cclay's), instant strong adhesion and cohesive failure by subsequent stretching were observed for almost all NC gels composed of different polymers or different Cclay values. A thermoresponsive NC gel was reversibly adhered and could be peeled from the surface by stretching (adhesive failure) at a temperature above its transition temperature. The mechanism of instant strong adhesion or reversible adhesion is discussed based on dangling chains that exist on the surfaces of the NC gels composed of polymer-clay networks. The cut surface of an NC gel generally exhibited a higher adhesive strength than the as-prepared surface because of longer dangling chains.