Orbit equivalence rigidity and bounded cohomology

We establish new results and introduce new methods in the theory of measurable orbit equivalence. Our rigidity statements hold for a wide (uncountable) class of negatively curved groups. Amongst our applications are (a) measurable Mostow-type rigidity theorems for products of negatively curved groups; (b) prime factorization results for measure equivalence; (c) superrigidity for orbit equivalence; (d) the first examples of continua of type II_1 equivalence relations with trivial outer automorphism group that are mutually not stably isomorphic.