  We survey Sorin Popa's recent work on Bernoulli actions. The paper was
written on the occasion of the Bourbaki seminar. Using very original methods
from operator algebras, Sorin Popa has shown that the orbit structure of the
Bernoulli action of a property (T) group, completely remembers the group and
the action. This information is even essentially contained in the crossed
product von Neumann algebra, yielding the first von Neumann strong rigidity
theorem in the literature. The same methods allow Popa to obtain II_1 factors
with prescribed countable fundamental group.
