This volume contains the proceedings of the 1st International Workshop on Artificial Intelligence and Easy and Plain Language in Institutional Contexts (AI & EL/PL 2025), held in conjunction with the 20th Machine Translation Summit (MT Summit 2025). The workshop aims to explore technological solutions focused on Easy and Plain Language across various institutional contexts and to bring together researchers from diverse fields, including healthcare, administrative communication, and education. It also aims to encourage multidisciplinary research that both develops and critically examines solutions and challenges related to promoting awareness of Easy and Plain Language, as well as advancing specialised machine translation and translation tools, including applications of large language models (LLMs) for translation.