We welcome your participation in the 15th International Conference on Gas in Marine Sediments (GIMS15). This gathering will take place in Cádiz, Spain, from Monday 23 to Friday 27 October, 2023 The GIMS conference series is a “grassroots” convergence where scientists and engineers from around the world openly discuss and debate cutting-edge issues related to gas in marine sediment. The conference series remains special because it is relatively small, because it includes a broad spectrum of people from fields, including geology, physics, biology, chemistry, and engineering, and because it strongly encourages collegiality and friendship to chase current and future topics of interest.