Introduction to little string theory

We start by describing the limit in which the dynamics of NS5-branes decouples from bulk physics. We discuss the holographic description of this limit and some of the properties of LST mentioned above. In particular, we exhibit some observables and physical states in the theory. We discuss the high energy thermodynamics of LST. We show that the spectrum has a Hagedorn growth and compute the Hagedorn temperature and the first subleading term in the entropy which shows that the thermodynamics is unstable. We introduce and study a class of vacua of LST which can be analyzed in a controlled weak coupling expansion. We add some comments on aspects of LST that we cannot treat in detail due to lack of time, including singularities of Calabi-Yau manifolds which give rise to d <6 dimensional vacua of LST and models with reduced supersymmetry, D-branes in the vicinity of NS5-branes, and instabilities in LST