Dubbed Nuit Debout (Up All Night), it is a self-styled "popular assembly" in which participants share views about politics and the state of the world.
As night descends, the speakers stand patiently in line and, turn by turn, take the microphone for their allotted five minutes.
Before them, sitting in twos and threes on paving stones, the young audience responds with the occasional cheer or boo.
Not that there is a huge amount to react to. The speeches are rambling and platitudinous.
One orator says the essence behind society should be "values" - but she does not say which.
Another urges an end to hierarchy - "no more pride, no more ego - just ideas".
A third wants to speak of human rights abuses in the Democratic Republic of Congo.
One theme that recurs is the need to tolerate divergences of opinion. This is significant. Two nights previously, one of France's best-known philosophers - a man who a generation ago would have himself been at the mike - was spat on and told to leave.
Both speakers and listeners appear to be mainly students - an impression confirmed by a tour of the various "stands".
The feminists are in a large huddle, and I am asked not to take photographs. Elsewhere, a screen shows a laborious film made by a woman who took a job distributing junk mail and wants to expose the exploitation.
There