  Consider two $k$-gons $P$ and $Q$. We say that the billiard flows in $P$ and
$Q$ are homotopically equivalent if the set of conjugacy classes in the
fundamental group of $P$ which contain a periodic billiard orbit agrees with
the analogous set for $Q$. We study this equivalence relationship and compare
it to the equivalence relations, order equivalence and code equivalence,
introduced in \cite{BT1,BT2}. In particular we show if $P$ is a rational
polygon, and $Q$ is homotopically equivalent to $P$, then $P$ and $Q$ are
similar, or affinely similar if all sides of $P$ are vertical and horizontal.
