Preface to the JOT Special Issue dedicated to Prof. Antonio Vallecillo on his 60th Birthday.

This special issue was born from an idea to thank Prof. Antonio Vallecillo, on the occasion of his 60th birthday, for his numerous contributions to the scientific community. We dedicate this collection of articles to an excellent professor, supervisor, leader, colleague and friend. The articles in this issue are related to software modeling, the main research area of Prof. Vallecillo.