The research area of Alef Sterk is the mathematical theory of dynamical systems. The general aim is to understand the long-term behaviour of nonlinear deterministic systems and qualitative changes in dynamics upon variation of system parameters. The transition from orderly to complex chaotic dynamics is particularly important. Rather than studying individual evolutions, the goal is to obtain a global and qualitative overview of the dynamics by studying the geometric organisation of the product of state and parameter spaces. Recently, I started working on the predictability and statistics of extreme events in deterministic systems with applications to weather and climate models.