The International Journal on Software Tools for Technology Transfer (STTT) has provided since 1997 a forum for research and experience papers on tools that support the development and verification of computer systems. STTT emphasizes work that takes rigorous, semantics-based, and formal approaches to tools and system development. To facilitate technology transfer and to offer a tool-oriented link between academic research and industrial practice, STTT seeks work that applies tools to realistic systems and that considers the broader workflows and tool chains needed to develop systems in industrial contexts. STTT also aims to build bridges between communities. Tool support for the development of reliable and correct computer systems is of growing importance: many design methodologies, analyses, verification techniques, and associated tools have been developed in different areas of computer science. However, despite some convergence in recent years, the involved areas still have their own culture and terminology, preventing researchers from taking advantage of the results obtained by colleagues in other fields. In fact, even complex tools from a certain field often reflect quite specific mindsets which hinder an open exchange. In 2020, STTT expanded its focus to include three new areas of emphasis called Themes that aim to break down some of these barriers and that address areas that the editorial board believes are especially open to impact from the rigorous approaches that have long been championed by STTT: (a) Explanation Paradigms Leveraging Algebraic Intuition, (b) Foundations for Mastering Change, and (c) Competitions and Challenges.