hold a chair along another activity, e.g. a consultant or entrepreneur giving lectures once or twice a week. Guest professors are international professors who take part in special lectures, classes or programme. Categories Grandes écoles can be classified into following broad categories: Écoles normales supérieures These schools train researchers and professors and may be a beginning for executive careers in public administration or business. Many French Nobel Prize and Fields Medal laureates were educated at the École Normale Supérieure in Paris, Lyon or Paris-Saclay. There are four ENS: the École Normale Supérieure of Paris, nicknamed "Ulm" from its address rue d'Ulm (Ulm Street) (sciences and humanities); the École Normale Supérieure de Lyon in Lyon (sciences and humanities); the École normale supérieure Paris-Saclay, near Paris (sciences, engineering, social sciences, economics and management, foreign languages). the École Normale Supérieure de Rennes near Rennes (sciences, engineering, social sciences, economics and management, sport). Until recently, unlike most other grandes écoles, écoles normales supérieures (ENS) did not award specific diplomas. Students who completed their curriculum were entitled to be known as "ENS alumni" or "normaliens". The schools encourage their students to obtain university diplomas in partner institutions while providing extra classes and support. Many ENS students obtain more than one university diploma. Normaliens from France and other European Union countries are considered civil servants in training (unless they were recruited by parallel admission), and as such are paid a monthly salary in exchange for agreeing to serve France for ten years, including those years spent as students. Engineering schools (grandes écoles d'ingénieurs) Many engineering schools recruit most of their students who have completed their education in scientific preparatory classes (2 years of post-baccalaureat study). Many are also joint graduate schools from several regional universities, sometimes in association with other international higher education networks. In France, the term 'engineer' has a broader meaning compared to the one understood in most other countries and can imply a person who has achieved a high level of study in both fundamental and applied sciences, as well as business management, humanities and social sciences. The best engineering schools will often provide such a general and very intensive education, although this is not always the case. Most of the schools of the following first four groups train the so-called 'generaliste' engineers: 1. Centrale Graduate Schools of engineering; its students are commonly known as pistons (a reference to the piston engine, one