Upsilon physics at CESR

Bound states of the heaviest known quark, the b-quark, provides us with a powerful laboratory for testing fundamental ideas in physics. Four 3S1 banti b bound states are now known to exist. Their masses and leptonic widths provide crucial information on the dynamics of quark binding. A large body of information has been collected in the past eighteen months at CESR on the four Y's. The Y'' was first resolved, the Y''' was discovered and proved to lie above the open flavor threshold. Finally, the first b-flavored particle, the pseudoscalar B-meson, was discovered by detecting its semileptonic decay. A brief description is given of the two detectors operating at CESR, and of heavy quark bound state phenomenology. Experimental results are presented and discussed in terms of current theoretical ideas. (orig.)