This book constitutes the proceedings of the 23rd International Conference on Comparative Genomics, RECOMB-CG 2026, held in Thessaloniki, Greece, during May 24&25, 2026.

The 19 full papers presented in this book were carefully reviewed and selected from 36 submissions. The papers are divided into the following topical sections: Combinatorics of Genome Rearrangements; Genome Evolution and Reconstruction; Phylogenetics I: Inferring Gene and Species Histories; Phylogenetics II: Comparing and Evaluating Phylogenies; Machine Learning in Genomics.