  In this thesis we study the AdS3 Wess-Zumino-Novikov-Witten model. We compute
the Operator Product Expansion of primary fields as well as their images under
the spectral flow automorphism in all sectors of the model by considering it as
a Wick rotation of the H3+ coset model. We argue that the symmetries of the
affine algebra require a truncation which establishes the closure of the fusion
rules on the Hilbert space of the theory. These results are then used to
discuss the factorization of four point functions by applying the bootstrap
approach.
  We also study the modular properties of the model. Although the Euclidean
partition function is modular invariant, the characters on the Euclidean torus
diverge and the regularization proposed in the literature removes information
on the spectrum, so that the usual one to one map between characters and
representations of rational models is lost. Reconsidering the characters
defined on the Lorentzian torus and focusing on their structure as
distributions, we obtain expressions that recover those properties. We then
study their generalized modular properties and use them to discuss the relation
between modular data and one point functions associated to symmetric D-branes,
generalizing some results from Rational Conformal Field Theories in the
particular cases of point like and dS2 branes, such as Cardy type solutions or
Verlinde like formulas.
