This book constitutes the proceedings of the 19th International Conference on Software and Systems Reuse, ICSR 2020, held in Hammamet, Tunesia in December 2020. Due to COVID-19 pandemic the Conference was held virtually. The 16 full papers and 2 short papers included in this book were carefully reviewed and selected from 60 submissions. The papers were organized in topical sections named: modelling, reuse in practice, reengineering, recommendation, and empirical analysis.