Most academic disciplines are based on a set of central theories. Software engineering has meanwhile produced few widely-accepted and influential theories of its core phenomena. TOSE consequently supports attempts to propose, synthesize, clarify and test theories of software engineering phenomena. TOSE especially promotes attempts to answer fundamental questions, integrate ideas from diverse sources and propose revolutionary, contrarian or ambitious new theories. We therefore invite papers proposing, extending or evaluating any kind of theory (e.g. causal, process, explanatory, predictive, descriptive) concerning any aspect of software engineering.