This book constitutes the refereed proceedings of the 51st International Conference on Software Technology: Methods and Tools, TOOLS 2019, held in Innopolis, Russia, in October 2019. The 19 revised full papers and 13 short papers presented in this book were carefully reviewed and selected from 62 submissions. The papers discuss all aspects of software engineering and programming languages; machine learning; internet of things; security computer architectures and robotics; and projects.