  We prove the $K(\pi,1)$ conjecture for affine Artin groups: the complexified
complement of an affine reflection arrangement is a classifying space. This is
a long-standing problem, due to Arnol'd, Pham, and Thom. Our proof is based on
recent advancements in the theory of dual Coxeter and Artin groups, as well as
on several new results and constructions. In particular: we show that all
affine noncrossing partition posets are EL-shellable; we use these posets to
construct finite classifying spaces for dual affine Artin groups; we introduce
new CW models for the orbit configuration spaces associated with arbitrary
Coxeter groups; we construct finite classifying spaces for the braided
crystallographic groups introduced by McCammond and Sulway.
