This volume contains papers of the 10th European Workshop on the Seismic Behaviour of Irregular and Complex Structures (10EWICS) held in Catania, Italy, in 2023. This international event provided a platform for discussion and exchange of ideas and unveiled new insights on the possibilities and challenges of irregular and complex structures under seismic actions. The topics addressed include criteria for regularity and design of buildings with structural irregularity/complexity, assessment and retrofit of buildings with structural irregularity/complexity, irregularity /complexity in high-rise buildings, historical constructions and bridges, soil-structure interaction and special cases of irregularity. Beyond an excellent number of interesting papers on these topics, this volume includes the paper of an invited lecture devoted to rocking seismic resisting systems with focus to concepts, analysis, design, and applicability to irregular buildings. The book is intented for all the community involved in the challenging task of seismic design, assessment and/or retrofit of irregular and complex structures.