This book constitutes the thoroughly refereed short papers, workshops and doctoral consortium papers of the 21th European Conference on Advances in Databases and Information Systems, ADBIS 2017, held in Nicosia, Cyprus, in September 2017. The 25 full and 4 short workshop papers and the 12 short papers of the main conference were carefully reviewed and selected from 160 submissions. The papers from the following workshops have been included in the proceedings: the first workshop on Data-Driven Approaches for Analyzing and Managing Scholarly Data, AMSD 2017; the first workshop on Novel Techniques for Integrating Big Data, BigNovelTI 2017; the first international workshop on Data Science: Methodologies and Use-Cases, DaS 2017; the second international workshop on Semantic Web for Cultural Heritage, SW4CH 2017.