This book constitutes the refereed proceedings of the 18th European Conference on Software Architecture, ECSA 2024, held in Luxembourg City, Luxembourg, during September 2-6, 2024. The 14 full research papers, 3 experience report papers, 7 short papers and 3 industry papers included in this book were carefully reviewed and selected from 89 submissions They were organized in topical sections as follows: Architecture modeling and design; Architecture evaluation; Microservices architecture; Sustainability; Trustworthiness; Architecture decision making; and Architecture documentation.