  We review physical motivations and possible realizations of string vacua with
large internal volume and/or low string scale and discuss the issue of
supersymmetry breaking. In particular, we describe the key features of
Scherk-Schwarz deformations in type I models and conclude by reviewing the
phenomenon of ``brane supersymmetry breaking'': the tadpole conditions of some
type-I models require that supersymmetry be {\it broken at the string scale} on
a collection of branes, while being exact, to lowest order, in the bulk and on
other branes.
