This book constitutes the proceedings of the 26th International Conference on Passive and Active Measurement, PAM 2025, held as a virtual event, during March 10-12, 2025. The 13 full papers and 7 short papers presented in this book were carefully reviewed and selected from 67 submissions. These papers cover a diverse range of topics, from 5G to IPv6, and from Web to Fraud. These papers have been categorized under the following topical sections: IPv6; Measurement Platforms; Web / HTTP; Connectivity; Routing; Anycast; Phishing and Fraud; 5G.