  We study the outer automorphism group of a right-angled Artin group
$A_\Gamma$ with finite defining graph $\Gamma$. We construct a subnormal series
for $Out(A_\Gamma)$ such that each consecutive quotient is either finite,
free-abelian, $GL(n,\mathbb{Z})$, or a Fouxe-Rabinovitch group. The last two
types act respectively on a symmetric space or a deformation space of trees, so
that there is a geometric way of studying each piece. As a consequence we prove
that the group $Out(A_\Gamma)$ is type VF (it has a finite index subgroup with
a finite classifying space).
  The main technical work is a study of relative outer automorphism groups of
RAAGs and their restriction homomorphisms, refining work of Charney, Crisp, and
Vogtmann. We show that the images and kernels of restriction homomorphisms are
always simpler examples of relative outer automorphism groups of RAAGs. We also
give generators for relative automorphism groups of RAAGs, in the style of
Laurence's theorem.
