The twenty-ninth edition of the Italian Symposium on Advanced Database Systems (SEBD Sistemi Evoluti per Basi di Dati) was organized by Università della Calabria, and held in Pizzo Calabro (Italy) from the 5th of September to the 9th of September 2021. The symposium is the major annual event of the Italian database research community at large, as it is thought of as a gathering forum to meet, discuss and exchange experiences among all those, both in the academy and industry, who are interested in database systems and in all their broad range of applications. The topics of SEBD 2021 covered the theoretical foundations, technology development, and real-world applications associated with database systems and related fields, including data integration, data inconsistency, NoSQL databases, knowledge management and ontologies, data mining, machine and deep learning, network analysis, cybersecurity. The programme of SEBD 2021 was organized into 18 sessions of oral presentations of 61 papers accepted at the end of a peer-reviewed process, and authored by researchers from 28 Italian universities and research institutes, 8 Italian companies, and 16 foreign universities and companies. The programme also included 2 invited tutorials, 3 keynote speeches by Stefano Ceri (Politecnico di Milano), Phokion G. Kolaitis (University of California at Santa Cruz and IBM Research), and Carlo Zaniolo (University of California at Los Angeles), and a panel discussion on “The Past and the Future of Computer Science Theory” with the participation of four distinguished computer science theorists (Ronald Fagin, Georg Gottlob, Christos Papadimitriou and Moshe Vardi), who were interviewed by Giorgio Ausiello, Maurizio Lenzerini, Luigi Palopoli, Domenico Saccà, and Francesco Scarcello. A joint seminar on “Reminiscence of TIDB 1981” was also held on the 9th of September, and organized in mixed online/in-presence sessions of invited lectures. Forty years ago, on September 13-19 of 1981, Gran Hotel San Michele hosted the progenitor of ICDT: the Advanced Seminar on Theoretical Issues in Databases (TIDB). We would like to thank all the contributing speakers for making SEBD 2021 a great event, and we are grateful to the members of our Steering, Technical Program, and Local Organization Committees, as well as ICT-SUD and Calabriatour.net for timely providing their support in all of the organizational and technical aspects.