Mental disorders and their symptoms are highly prevalent in the university student population, and the transition from secondary to tertiary education is associated with a rise in mental health problems. Existing web-based interventions for the prevention of common mental disorders in student populations often focus on just one disorder and have not been designed specifically for students. There is thus a need for transdiagnostic, student-specific preventative interventions that can be widely disseminated. This two-arm, parallel group randomised controlled trial aims to evaluate the effectiveness and cost-effectiveness of a web-based transdiagnostic mental health problem prevention programme (PLUS) across several universities in four countries.