  The Pre-Big Bang cosmology inspired generations of cosmologists in attempts
to cure the initial Big Bang singularity using a fundamental length scale as
proposed by String Theory. The existence of a phase of collapse/inflation with
increasing curvature followed by a cosmic bounce has been proposed as an
alternative to standard inflation in the solution of the horizon and curvature
problems. However the generation of a nearly scale-invariant spectrum of
perturbations is not an automatic prediction of such scenarios. In this paper I
review some general statements about the evolution of perturbations in bouncing
cosmologies and some historically significant attempts to reconcile the
predicted spectra with the observations. Bouncing cosmologies and in particular
the Pre-Big Bang scenario stand as viable, although more complicated,
alternatives to inflation that may still help solve current theoretical and
observational tensions.
