A target-focused library is a screening collection of compounds specifically tailored to modulate the function of a particular target or a protein family. These libraries not only reduce waste by eliminating compounds that are unlikely to bind to target proteins, but often lead to the increased potency and specificity of binders, as demonstrated for c-Src kinase. Compared to large and diverse screening libraries, using relatively small and targeted collections significantly improves the odds of finding potential drug candidates, thus further reduces the costs of drug discovery.