This book constitutes the proceedings of the 9th European Interdisciplinary Cybersecurity Conference, EICC 2025, which took place in Rennes, France, during June 18-19, 2025. The 21 full papers and 2 short papers included in these proveedings were carefully reviewed and selected from 39 submissions. They were organized in topical sections as follows: Artificial intelligence applied to cybersecurity; cybercrime and cyberthreats; cybersecurity; software development security; advances in interdisciplinary cybersecurity: insights from funded reserach projects - CyFRP 2025 special session; complex network analysis for cybersecurity - CNACYS 2025 special session; medical device security and privacy - MeDSec 2025 special session; MDCG guidance; threshold multiparty private set intersection.