Introduction to string theory

This article is an introduction to string theory covering basic principles as well as advanced applications. The fundamental ideas behind string theory and how they are mathematically implemented is reviewed. The bosonic string is discussed and its problems are outlined. The five consistent superstring theories are introduced as well as their recently discovered relations through dualities. The black hole information paradox and how it is resolved by string theory is explained. There is also discussion about how ideas like holography and M-theory can lead us to physics beyond string theory. Finally, there is a brief review of the recent ideas of large extra dimensions that might lead to new possiblities for the experimental verification of string theory.