Supersymmetry and grand unification

Supersymmetry and Grand Unification are the two most promising directions for physics beyond the Standard Model. They receive indirect experimental support from the apparent lightness of the Higgs boson, the values of the gauge couplings measured at LEP and elsewhere, and the persistent solar neutrino deficit. Phenomenological constraints and theoretical models constrain predictions in interesting ways. All these ideas may be embedded in string theory, which is shown by newly-discovered dualities to possess previously-unsuspected richness and simplicity.