Double Field Theory, T-Duality, and Courant Brackets

These lecture notes are based on three lectures, each ninety minutes long, given by the author at the "International School on Strings and Fundamental Physics" which took place in Garching/Munich from July 25 to August 6, 2010. These lectures, aimed at graduate students, require only a basic knowledge of string theory and give a simple introduction to double field theory. These notes were prepared by Marco Baumgartl and Nicolas Moeller.