Abstract. We are developing a methodology of Test-Driven Development of Models (TDDM) based on an experimental UML2.0 modeling tool SMART. Our experience shows that TDDM is quite useful for agile model developments. SMART provides guidance how to build models based on compiler errors of testcases, something similar to what Quick Fix of Eclipse does. It also provides such guidance even from failures of testcases, which seems di cult in the case of TDD of programs.