The basic requirements for the compounds that are supposed to penetrate the blood-brain barrier are somewhat different from those for the majority of drug discovery projects. Alongside the known problem with delivery of the large and non-polar compounds and their penetrability through the cell membrane, the other issue arises as well: small and polar compounds are not able to pass the Blood-Brain Barrier. Chemspace CNS-focused library comprises quite small, non-polar compounds that are also free from PAINS/toxic fragments and aggregators.