Geosynthetic clay liners (GCLs) are commonly used in geocomposite waste barrier systems as replacement for compacted clay liners. In recent years a number of problems associated with GCLs have been identified including panel shrinkage, desiccation cracking, chemical incompatibility, cation exchange and lack of hydration in geomembrane/GCL composite liner systems. The most important factor affecting the performance of a GCL is cation exchange in the bentonite. Leachate compatibility testing of the GCL is therefore necessary, initially by swell index testing, followed by hydraulic conductivity testing if the swell index test indicates promising results. The results of leachate GCL compatibility testing performed for four waste disposal facilities are presented and their influence on the respective barrier designs. It is concluded that there is a future for the use of GCLs in waste barrier systems provided that the compatibility of the GCL is confirmed through testing