These proceedings are the outcome of the 63rd ESReDA Seminar on "Resilience assessment: Methodological challenges and applications to critical infrastructures" that took place at the European Commission's Joint Research Centre's (JRC) premises in Ispra, Italy, on 25-26 October 2023. A broad spectrum of resilience topics were covered, with sessions addressing different infrastructure sectors: energy sector (electricity, gas, hydrogen), transport sector (rail, road, air and maritime), other critical infrastructures, networks and entities, urban development, public sector and government. The seminar aimed at addressing resilience due to different hazards or threats, such as: disruptions of infrastructures due to aging or technical failures, natural events, intentional attacks or emerging threats, hybrid being an example. This seminar brought together researchers, practitioners and decision-makers from academia, operators, industry, governing bodies, to discuss theories, concepts, and experiences of resilience assessment methodologies and applications. The proceedings include 3 plenary speeches and 25 full papers or extended abstracts.