  Recently, a new framework for solving the hierarchy problem has been proposed
which does not rely on low energy supersymmetry or technicolor. The
gravitational and gauge interactions unite at the electroweak scale, and the
observed weakness of gravity at long distances is due the existence of large
new spatial dimensions. In this letter, we show that this framework can be
embedded in string theory. These models have a perturbative description in the
context of type I string theory. The gravitational sector consists of closed
strings propagating in the higher-dimensional bulk, while ordinary matter
consists of open strings living on D3-branes. This scenario raises the exciting
possibility that the LHC and NLC will experimentally study both ordinary
aspects of string physics such as the production of narrow Regge-excitations of
all standard model particles, as well more exotic phenomena involving strong
gravity such as the production of black holes. The new dimensions can be probed
by events with large missing energy carried off by gravitons escaping into the
bulk. We finally discuss some important issues of model building, such as
proton stability, gauge coupling unification and supersymmetry breaking.
