We consider a two level system, $\mathcal{S}_{2}$, coupled to a general $n$
level system, $\mathcal{S}_{n}$, via a random matrix. We derive an integral
representation for the mean reduced density matrix ${\rho} (t)$ of
$\mathcal{S}_{2}$ in the limit $n\to \infty $, and we identify a model of
$\mathcal{S}_{n}$ which possesses some of the properties expected for
macroscopic thermal reservoirs. In particular, it yields the Gibbs form for
${\rho} (\infty)$. We consider also an analog of the van Hove limit and obtain
a master equation (Markov dynamics) for the evolution of $\rho (t)$ on an
appropriate time scale.