Abstract: The purpose of this talk is to present some recent results about phase transitions in the Cuntz c-star algebra due to K. Thomsen. We would like to briefly review some of the main concepts of c-star algebras and their construction from a given grupoid. In the case of the Cuntz algebra, the grupoid is related to a symbolic dynamical system and so dynamical ideas are useful to describe the KMS states and how they depend from a certain parameter.