What is Ecole Normale Supérieure?

The French "Grandes Ecoles" system of higher education is very difficult to understand for foreigners. Pointing out the features that are unique to that system only creates perplexity and confusion. Instead, let me point out some features that are common with some schools in the US (the other system with which I am familiar).

Consider the "Ecole Normale Supérieure de la rue d'Ulm", quite a mouthful of a name! (It is also called "Ecole Normale Supérieure", "ENS", "ENS Ulm", "rue d'Ulm", or "Ulm" for short.)

It is old, dating from the late 18th century. Part of its fame comes from famous alumni in its long history. It has developed its own vocabulary and traditions.

It is primarily famous for its "undergraduate" students (roughly). For example, the totality of French-raised Fields medalists are ENS alumni, but their PhDs were obtained at a variety of universities, and their research work as graduate students was not done in the labs of ENS. As far as I can tell: Strasbourg (Schwartz, Thom), Sorbonne (Serre), Paris 6 (Connes, Lions, Werner), Ecole Polytechnique (Yoccoz), Paris 11 (Lafforgue), Paris-Dauphine (Villani).

It has sister schools that are independent of it but that have roughly similar goals and structure: ENS Lyon (also sometimes called "ENS" in context, for example when one is in the town of Lyon) and ENS Cachan.

It teaches academic subjects covering the spectrum of arts and sciences. No preeminence is given to science over the humanities.

It is tiny: only 2200 students! ENS Cachan and ENS Lyon are similarly small.

Traditionally it largely left students free to learn whatever they wanted and to follow their intellectual pursuits in whatever way they wanted, with the idea that they could be trusted to do something worthwhile with that great freedom. (But it is not clear how much of that tradition still exists nowadays.)

It is the best in its category: no student accepted at ENS ever turns it down, except for some scientists who choose to go to Ecole Polytechnique instead. (Ecole Polytechnique is for sciences only and has a different style)

Many of the students are very, um, aware that they "are the best"...

So I think that someone from the US and who would be looking for a rough and simple analogy could consider that ENS Ulm, ENS Lyon and ENS Cachan are the French Ivy League schools, and, among those, consider that ENS is the French Harvard. (Similarly one might perhaps consider that Ecole Polytechnique is analogous to CalTech.)

The single most outstanding difference between ENS and Harvard lies in their mission: Harvard educates students to serve society, but the particular ways in which they will serve are left undefined. In contrast, the three ENS schools (Ulm, Cachan, Lyon) exist to educate students who will serve society in well-defined careers: the students are primarily future academics, teachers, and researchers. (Thus, for example, Ivy League schools recruit students with excellent grades but who also additionally show some other, non-academic potential, whereas the ENS schools recruit solely on the basis of academic performance.)

The next most important difference is financial. The ENS are public, and the French state aims to offer the best possible conditions to help its most promising young people become leading academics: one way in which it does that is by paying for their studies for 4 years (in return, the students commit to serve the state for 10 years.) That is, the ENS pays the students, whereas Harvard asks the students to pay.