To understand life's processes, perturb them. How a process responds to an insult can provide clues about normal function or mimic a specific disease state. Gene mutation is one powerful perturbation method. Dr. Schreiber discusses a newer approach, called chemical genetics, that uses small molecules to bypass genes and perturb proteins directly. He illustrates the approach with the small molecule furrowstatin, which interrupts the process of cell division. Dr. Schreiber also explains diversity-oriented synthesis, a process that can rapidly create thousands of different molecules. He discusses the molecular screening methods needed to identify which of thousands of molecules may be useful for understanding a protein's function—or even for developing a new medicine.