This book constitutes the refereed proceedings of the tracks and workshops which complemented the 15th European Conference on Software Architecture, ECSA 2021, held in Vaxjoe, Sweden*, in September 2021. The 15 full papers presented in this volume were carefully reviewed and selected from 17 submissions. Papers presented were accepted into the following tracks and workshops: Industry Track; DE&I - Diversity, Equity and Inclusion Track; SAEroCon - 8th Workshop on Software Architecture Erosion and Architectural Consistency; MSR4SA - 1st International Workshop on Mining Software Repositories...