The chromosphere is the interface between the interior of the Sun, where its magnetic field is generated, and the hot outer corona that drives the solar wind and causes space weather. It is difficult to understand: the chromosphere is the interface where the dynamics change from gas-pressure driving to magnetic-force driving, radiation transport changes from optically thick to optically thin, the gas state changes from neutral to ionised and from local thermodynamic equilibrium (LTE) to non-equilibrium conditions, and the MHD approximation is not sufficient to fully describe its physics. In this talk I will give an overview of the major open questions on understanding the solar chromosphere, and dicuss how observations, simulations, and advanced analysis tools can be used to shed light on these questions.