The 9th International Symposium on Molecular Aspects of Catalysis by Sulfides (MACS IX) will take place in Visegrád, Hungary, on May 23-27, 2027, organized by the HUN‑REN Centre for Energy Research. Building on more than two decades of MACS meetings that connect academia and industry, the symposium returns after a pandemic‑related pause with renewed momentum. The program spans the field—from hydrotreating and new catalyst preparation routes to in situ/operando characterization, computational catalysis, and the emerging roles of sulfides in electrochemical and photoelectrochemical energy conversion and CO₂ reduction. Join us in Visegrád to help set the agenda for the next wave of sulfide catalysis research.