  How far can a stack of $n$ identical blocks be made to hang over the edge of
a table? The question dates back to at least the middle of the 19th century and
the answer to it was widely believed to be of order $\log n$. Recently,
Paterson and Zwick constructed $n$-block stacks with overhangs of order
$n^{1/3}$, exponentially better than previously thought possible. We show here
that order $n^{1/3}$ is indeed best possible, resolving the long-standing
overhang problem up to a constant factor.
