We hear to talk about substances like cholesterol, adrenalin, penicillin, aspirin, caffeine, nicotine, TNT or vitamin C every day. For those who want to know better this kind of molecules, the Common Molecules Collection is the ideal place. The authors focused their attention on molecules studied in chemistry classrooms but this fascinating collection includes also molecules that might be of interest for the general public. For each molecule, its structure is presented together with some additional information. In this site, organized in a very elegant way, there is also helpful information about crystallography and crystallization.