In his PhD thesis he developed and proved correct the first sound type system for ML-style polymorphic references, an important open problem at the time.
Mads Tofte is a co-author of the Definition[2] of Standard ML and the associated Commentary, probably the most precise description developed for any realistic programming language.
Subsequently, he developed (with Jean-Pierre Talpin) the notion of region inference, a program analysis and memory management technique that avoids or minimizes the use of garbage collection.
In the late nineties he co-developed (with Fritz Henglein and others) a type system and a sophisticated tool called AnnoDomini for mitigation of the Year 2000 problem in COBOL software.
He oversaw the creation of the university from scratch, the hiring of faculty/staff, recruitment of students and the design of the study programs.