Analytical pharmacology strives to compare pharmacological data to detailed quantitative models. The most famous tool in this regard is the Black/Leff operational model, which can be used to quantify agonism in a test system and predict it in any other system. Here we give examples of how and where analytical pharmacology has been used to classify drugs and predict mechanism of action in pharmacology. We argue for the importance of analytical pharmacology in drug classification and in prediction of drug mechanisms of action. Although some of the specifics of Black's models have been updated to account for new developments, the principles of analytical pharmacology should shape drug discovery for many years to come.