This book constitutes the refereed proceedings of the 23rd European Conference on Genetic Programming, Euro GP 2020, held as part of Evo*2020, in Seville, Spain, in April 2020, co-located with the Evo*2020 events Evo COP, Evo MUSART and Evo Applications.The 12 full papers and 6 short papers presented in this book were carefully reviewed and selected from 36 submissions. The papers cover a wide spectrum of topics, including designing GP algorithms for ensemble learning, comparing GP with popular machine learning algorithms, customising GP algorithms for more explainable AI applications to real-world problems.