  The paper considers ribbon tilings of large regions and their per-tile
entropy (the logarithm of the number of tilings divided by the number of
tiles). For tilings of general regions by ribbon tiles of length $n$, we give
an upper bound on the per-tile entropy as $n - 1$. For growing rectangular
regions, we prove the existence of the asymptotic per-tile entropy and show
that it is bounded from below by $\log_2 (n/e)$ and from above by $\log_2(en)$.
For growing generalized "Aztec Diamond'' regions and for growing "stair''
regions, the asymptotic per-tile entropy is calculated exactly as $1/2$ and
$\log_2(n + 1) - 1$, respectively.
