Professor Marklof has made deep and long-lasting contributions at the interface between ergodic theory, mathematical physics and number theory. His main achievements include the proof of the Berry-Tabor conjecture for an important class of integrable billiards, his resolution with Strömbergsson of the long-standing and important problem of determining the nature of the stochastic process that emerges in the Boltzmann-Grad limit of the periodic Lorentz gas, the characterization of the limit distributions of theta sums and Frobenius numbers, and highly influential contributions to the mathematical theory of quantum chaos.