The present book includes a set of selected papers from the 11th International Conference on Simulation and Modeling Methodologies, Technologies and Applications (SIMULTECH 2021) that was held as an online event, from July 7 to 9, 2021. The conference brought together researchers and practitioners interested in methodologies and applications of modeling and simulation. New and innovative solutions are reported in this book. A selection was made after the conference, based also on the conference chairs assessment, reviewers' assessment, quality of presentation and audience interest, so that this book includes the extended and revised versions of the very best papers of the conference.