Phase change processes of supercooled droplets at different boundary conditions are presented. This study is a summary of the current developments within subproject B1 of the SFB-TRR 75 with the focus on evaporation, sublimation, and freezing of supercooled droplets. To this end, new numerical methods to describe the phase transition were developed and novel strategies dealing with the challenges of droplets under extreme conditions are presented. The numerical solution procedure of all phase changes are summarized in a compact way within this work. In order to validate the numerical models, experiments were conducted. For this, new experimental setups and approaches were developed. These comprise a test chamber for optical levitation of supercooled droplets, which is able to trap a droplet by means of a laser beam at subzero temperatures and variable ambient humidity. Comparisons of the numerical simulations and the conducted experiments are presented for several phase change processes. The results are in very good agreement and proof the capability of the methods.