This volume LNCS 14300 constitutes the refereed proceedings of the 18th International Conference, IFM 2023, in November 2023, held in Leiden, The Netherlands. The 16 full papers presented together with 2 short papers were carefully reviewed and selected from 51 submissions. The conference focuses on all aspects of the design of integrated techniques, including language design, verification and validation, automated tool support, and the use of such techniques in software engineering practice.