  Given a domain $\Omega$ in $\mathbb{C}^m$, and a finite set of points
$z_1,\ldots, z_n\in \Omega$ and $w_1,\ldots, w_n\in \mathbb{D}$ (the open unit
disc in the complex plane), the $Pick\, interpolation\, problem$ asks when
there is a holomorphic function $f:\Omega \rightarrow \overline{\mathbb{D}}$
such that $f(z_i)=w_i,1\leq i\leq n$. Pick gave a condition on the data $\{z_i,
w_i:1\leq i\leq n\}$ for such an $interpolant$ to exist if $\Omega=\mathbb{D}$.
Nevanlinna characterized all possible functions $f$ that $interpolate$ the
data. We generalize Nevanlinna's result to an arbitrary set $\Omega$. In this
case, the function $f$ comes from the Schur-Agler class. The abstract result is
then applied to three examples - the bidisc, the symmetrized bidisc and the
annulus. In these examples, the Schur-Agler class is the same as the Schur
class.
