  Determining unknotting numbers is a large and widely studied problem. We
consider the more general question of the unknotting number of a spatial graph.
We show the unknotting number of spatial graphs is subadditive. Let $g$ be an
embedding of a planar graph $G$, then we show $u(g) \geq \max\{u(s) |$ $s$ is a
non-overlapping set of constituents of $g\}$.
  Focusing on $\theta$-curves, we determine the exact unknotting numbers of the
$\theta$-curves in the Litherland-Moriuchi Table. Additionally, we demonstrate
unknotting crossing changes for all of the curves. In doing this we introduce
new methods for obstructing unknotting number $1$ in $\theta$-curves.
