G-protein coupled receptors (GPCRs) represent possibly the most important target class of proteins for drug discovery. Over 30% of clinically marketed drugs are active at this receptor family. These drugs exhibit their activity at <10% of all known GPCRs. A major challenge for the pharmaceutical industry is to associate the many novel GPCRs with disease to identify the drugs of the future. This process consists of a collection of experimental paradigms that together can be loosely labelled 'target validation'.