Dear Colleagues, we announce the fourth edition of the Galileo Gailiei Institute PhD School on: "Theoretical Aspects of Astroparticle Physics, Cosmology and Gravitation" to be held at The Galileo Galilei Institute of Theoretical Physics, Arcetri, Florence (Italy) from 20 to 31 March, 2023. Details can be found at the page: agenda.infn.it/e/apcg2023