  Cosmological models involving a bounce from a contracting to an expanding
universe can address the standard cosmological puzzles and generate
"primordial" density perturbations without the need for inflation. Some such
models, in particular the ekpyrotic and cyclic models that we focus on, fit
rather naturally into string theory. We discuss a number of topics related to
these models: the reasoning that leads to the ekpyrotic phase, the predictions
for upcoming observations, the differences between singular and non-singular
models of the bounce as well as the predictive and explanatory power offered by
these models.
