Foreword: In memory of Assyr Abdulle 1971–2021

Assyr received his Ph.D. in 2001 on "Chebyshev Methods Based on Orthogonal Polynomials" which allow explicit Runge-Kutta methods to remain stable for large time steps while increasing the number of stages.He then did a PostDoc with Bjorn Engquist and Weinan E at Princeton in 2001-2002, where he started working on Heterogeneous Multiscale Methods, and another PostDoc at ETHZ in 2002-2003 with Christoph Schwab.He then got an assistant professorship at the University of Basel in 2003, and became associate professor at the University of Edinburgh in 2007, where he started working on stochastic equations.Finally, he came to EPFL in 2010.Assyr was a world-renowned expert in the field of numerical methods for ordinary and stochastic differential equations, and multiscale problems, where he made numerous landmark contributions.