The work "Machine Learning and Knowledge Discovery in Databases" includes the refereed proceedings of the European Conference on Machine Learning and Knowledge Discovery in Databases (ECML PKDD 2018), which took place in September 2018 in Dublin, Ireland. The three volumes, published under LNAI numbers 11051 to 11053, contain a total of 131 regular contributions, carefully selected from 535 submitted papers. The contributions are divided into various thematic sections covering a wide range of topics in the field of machine learning and data analysis. This publication is aimed at professionals and researchers engaged with the latest developments and applications in machine learning, data science, and related disciplines. The diversity of topics addressed ranges from adversarial learning to deep learning and recommender systems, providing a comprehensive overview of current trends and challenges in data analysis.