In the present thesis, we will review various Bethe ansatz techniques such as the (nested)\nalgebraic Bethe ansatz and the (nested) coordinate Bethe ansatz using well known models\nlike the XXX model and the Hubbard model. Subsequently, the Bethe ansatz techniques\nare applied to obtain Bethe ansatz equations and Bethe vectors of the su(2|2)-invariant S -\nmatrix. Finally, these results are used to obtain the full S -matrix and Bethe equations of the\nstring sigma model.