A Master of Advanced Studies (MAS) is a graduate degree in various countries.
The DEA was generally considered the Master's degree in the French-speaking countries and it was sometimes referred to as a "first doctoral diploma".
In France the DEA was a 1-2 years degree taken after a maîtrise (4-years French master's degree) and was prior to entering a doctoral program. It was generally equivalent to the North American "All But Dissertation" or ABD status within a doctoral program or a Master of Philosophy (M.Phil.) or Master of Research (M.Res.) degree. But in the French-speaking universities in Switzerland the DEA was equivalent to the Master's degree in the Anglo-Saxon countries, and it was a 1-2 years degree taken after a Licence (4 years Swiss undergraduate degree).
The DEA and DESS exist in many places which apply the French university style and sometimes with some minor differences such as Quebec, Belgium, Luxembourg, Spain, Algeria, Morocco, Lebanon, Tunisia and most Francophone countries.
It generally consisted of a number of courses, with examinations and grades, followed by research in a scientific laboratory. The students would then write a substantial thesis about the scientific work they did, and defend this thesis in front of a committee. In Europe, the DEA's degrees are progressively subsumed into the Bologna process Master's degrees and research-oriented (Master of Advanced Studies).