  We derive strain-gradient plasticity from a nonlocal phase-field model of
dislocations in a plane. Both a continuous energy with linear growth depending
on a measure which characterizes the macroscopic dislocation density and a
nonlocal effective energy representing the far-field interaction between
dislocations arise naturally as scaling limits of the nonlocal elastic
interaction. Relaxation and formation of microstructures at intermediate scales
are automatically incorporated in the limiting procedure based on
$\Gamma$-convergence.
