  The Chen groups of a group $G$ are the lower central series quotients of the
maximal metabelian quotient of $G$. Under certain conditions, we relate the
ranks of the Chen groups to the first resonance variety of $G$, a jump locus
for the cohomology of $G$. In the case where $G$ is the fundamental group of
the complement of a complex hyperplane arrangement, our results positively
resolve Suciu's Chen ranks conjecture. We obtain explicit formulas for the Chen
ranks of a number of groups of broad interest, including pure Artin groups
associated to Coxeter groups, and the group of basis-conjugating automorphisms
of a finitely generated free group.
