A laboratory investigation was conducted to determine moisture-suction relationships for geosynthetic clay liners (GCLs) as a function of GCL type and hydration solution. The moisture-suction relationships were then used to estimate various engineering properties of the GCLs under unsaturated conditions. Predictions of the permeability function and the shear strength function for the GCLs are presented herein. The shapes of the permeability and shear strength functions were influenced by the air-entry suction value and the hysteresis of the corresponding moisture-suction relationships. Significant variations were observed in the estimated engineering behavior of the GCLs as a function of hydration solution, whereas relatively insignificant variations were observed as a function of GCL type. Moisture-suction relationships determined under representative test conditions may be used to estimate field performance of GCLs for applications such as barrier systems for solid and liquid waste containment facilities; liner systems for liquid containment structures such as ponds, impoundments, reservoirs, and water conveyance canals; covers for various containment systems; as well as for agricultural applications.