Willem van Zwet made deep and influential contributions to probability and statistics, which we review in this paper. Bickel and Götze collaborated with him on his major contributions to higher order asymptotics of nonlinear statistics and on resampling and the bootstrap. We relate this work to his remarkable development of the properties of the Hoeffding expansion for symmetric statistics as well as Fourier analytic tools. Fiocco and De Gunst were his students. We describe how in their theses and subsequent papers with him they developed statistical inference in two subtle stochastic models, the contact process and cell population development under a plausible regime. We also touch on his solutions of intriguing problems not related directly to his main interests.