This thesis provides a number of examples of changing cofinalities of cardinals using forcing. The main emphasis is put on the forcing notion developed by Prikry, which is used to change the cofinality of a measurable cardinal kappa to omega, while preserving all other cardinals and the universe below kappa . It is shown that the assumption of measurability cannot be weakened. Next, two variations of the original Prikry forcing are explored. Finally, a forcing notion developed by Namba is introduced, which makes the only nontrivial change of cofinality without assuming any large cardinal properties.
