In this session, we aim to bring together observers and theorists to discuss recent developments regarding planetary atmospheric escape as well as the radiation, plasma, and magnetic environments of planetary systems. Many questions remain to be addressed regarding the state of close-in exoplanet atmospheres and of their interactions with the host star. Observations and studies of atmospheric escape can bring crucial information about both planets and their star. They further suggest that this mechanism can significantly impact the evolution and potential habitability of close-in planets. This session will thus put a special focus on escaping exoplanet atmospheres and their observational signatures, welcoming contributions on topics related to planetary system evolution, stellar and planetary wind interactions, stellar plasmas and radiative impacts on planetary environments. We will discuss which observing and modeling tools are available, or should be developed, to study these phenomena.