The objectives of the paper are: (1) to provide an introduction to GCLs (Geosynthetic Clay Liners) for those who may be unfamiliar with this lining material; (2) to summarize the potential applications of GCLs to landfill covers; (3) to examine the relative advantages and disadvantages of GCLs compared to compacted clay liners; and (4) to provide a genetic assessment of performance equivalency of GCLs compared to low-permeability, compacted clay barriers. The fourth item will comprise the bulk of the paper. The conclusion is drawn that geosynthetic clay liners can be shown to provide equivalent performance to low-permeability, compacted clay liners for many landfill sites. The key issues concerning equivalency are ability to limit percolation of water through the barrier, permeability to gas, slope stability, and puncture resistance.