Abstract Conventional adhesives experience reduced adhesion when exposed to aqueous environments. The development of underwater adhesives capable of forming strong and durable bonds across various wet substrates is crucial in biomedical and engineering domains. Nonetheless, limited emphasis placed on retaining high adhesion strengths in different saline environments, addressing challenges such as elevated osmotic pressure and spontaneous dimensional alterations. Herein, a series of ionogel‐based underwater adhesives are developed using a copolymerization approach that incorporates “dynamic complementary cross‐linking” networks. Synergistic engineering of building blocks, cross‐linking networks, pendant groups and counterions within ionogels ensures their adhesion and cohesion in brine spanning a wide salinity range. A high adhesion strength of ≈3.6 MPa is attained in freshwater. Gratifyingly, steady adhesion strengths exceeding 3.3 MPa are retained in hypersaline solutions with salinity ranging from 50 to 200 g kg −1 , delivering one of the best‐performing underwater adhesives suitable for diverse saline solutions. A combination of outstanding durability, reliability, deformation resistance, salt tolerance, and self‐healing properties showcases the “self‐contained” underwater adhesion. This study shines light on the facile fabrication of catechol‐free ionogel‐based adhesives, not merely boosting adhesion strengths in freshwater, but also broadening their applicability across various saline environments.

Deformation‐Resistant Underwater Adhesion in a Wide Salinity Range