The ICSLS (InternationaI Conference on Spectral Line Shapes) bi-annual conference series started in Paris, France in 1973, and it is held alternating European and North-American locations. The last three editions were held in Tullahoma, Tennessee, USA (2014), Torun, Poland (2016) and Dublin, Ireland (2018). The 25th ICSLS conference is organized by the Department of Mathematics and Physics, University of Campania Luigi Vanvitelli. It will be held inside the wonderful Monumental Complex of Belvedere di San Leucio, in Caserta (Italy). Also known as Ferdinandopoli, its construction is due to king Ferdinand IV of Bourbon, who wished to create a small village around the silk factory, in the eighteenth century. The ICSLS 2020 conference covers a broad range of topics related to spectral line shape studies, including: line shapes of atomic and molecular transitions in neutral gaseous mixtures, fundamental metrology, single and multi-photoionisation processes, high and low temperature plasmas, clusters and helium droplets, nanophotonic processes, spectroscopy of stellar atmospheres and interstellar media, spectroscopy of planetary atmospheres and exoplanets, cold atoms and molecules, collision-induced spectra, processes in laser fields, innovative techniques of line shape applications for diagnostic purposes and fundamental studies with narrow optical resonances, along with applications in e.g., industrial, environmental, medical and all other potential domains of interest. The conference will include a mix of invited lectures, contributed talks and poster presentations.