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**Neven Bilić** String theory, which has been the main candidate for a fundamental theory of the universe for more than 20 years, is believed to be a unique theory that unifies all the particles and forces in nature -- including gravity. But even if the theory is unique, the number of different universes that appear as solutions to its equations is enormous. One interpretation of this unpleasant feature is that we live in one of many worlds comprising the so called //multiverse//. Besides, consistency of string theory requires existence of multidimensional objects -- $D$-branes, which opens a possibility that our universe is a $3+1$ dimensional brane --- the so called "braneworld" --- moving in a $4+1$ dimensional bulk. Astrophysical and cosmological implications of the string-theory multiverse and braneworlds will be discussed.