  Jets in the vacuum correspond to multi-parton configurations that form via a
branching process sensitive to the soft and collinear divergences of QCD. In
heavy-ion collisions, energy loss processes that are stimulated via
interactions with the medium, affect jet observables in a profound way. Jet
fragmentation factorizes into a three-stage process, involving vacuum-like
emissions above the medium scale, induced emissions enhanced by the medium
length and, finally, long-distance vacuum-like fragmentation. This formalism
leads to a novel, non-linear resummation of jet energy loss. In this talk we
present new results on the combined effects of small-$R$ resummation and energy
loss to compute the $R$-dependent jet spectrum in heavy-ion collisions.
