About 90 years ago, just after the great revolutions of relativity and quantum mechanics, H. Weyl and W. Pauli expressed serious concerns about the possibility of constructing a truly unified theory of space, time, and matter. I will give my personal view on the status of this issue in the light of the successes and puzzles of our present “Standard Model of Nature” and of some 40 years of exciting/frustrating work in string theory.

College de France and CERN