This book constitutes the proceedings of the 25th International Conference on Conceptual Structures, ICCS 2020, held in Bolzano, Italy, in September 2020.* The 10 full papers, 5 short papers and 1 poster paper presented were carefully reviewed and selected from 24 submissions. The proceedings also include two keynotes and two tutorials. The papers focus on the representation of and reasoning with conceptual structures in a variety of contexts. The topics of this year's conference range from formal concept analysis to decision making, from machine learning to natural language processing. *The conference was held virtually due to the COVID-19 pandemic.