The 9th International Symposium on Molecular Aspects of Catalysis by Sulfides (MACS IX) will take place in Visegrád, Hungary, in 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.