  In this paper we study the Martin boundary of open sets with respect to a
large class of purely discontinuous symmetric L\'evy processes in ${\mathbb
R}^d$. We show that, if $D\subset {\mathbb R}^d$ is an open set which is
$\kappa$-fat at a boundary point $Q\in \partial D$, then there is exactly one
Martin boundary point associated with $Q$ and this Martin boundary point is
minimal.
