I believe that the genetic code was the greatest discovery of the 20th century (Fig. 1). The code was worked out during the period that I was a student: a medical student at Tufts University (I dropped out after a year), a graduate student at MIT and Cornell (with Gordon Hammes), and a postdoctoral student at Stanford University (with Paul Flory). My research as a student was centered on theoretical and experimental physical chemistry, as applied to biological systems. With Hammes, I had done a spectroscopic and thermodynamic analysis of ribonuclease and its interaction with one of its ligands. I also had done both experimental and theoretical analyses of kinetic relaxation spectroscopy, inspired in part by the pioneering work of Eigen, who himself had been a mentor of Hammes. (Eigen gave lectures at Cornell that I attended, and we spent time in conversation as well. In more recent years, we have seen each other on a regular basis and continued our conversations.) With Flory at Stanford, I worked on statistical mechanics of polypeptides. All of that graduate and postdoctoral work was exciting, particularly the mathematical side that I especially loved because of its elegance, rigor, and abstraction. However, while this sort of mental activity was going on, I kept thinking about the newly discovered genetic code and aminoacyl-tRNA synthetases.