This text deals with certain algebraic and arithmetical questions concerning polynomial mappings in one or several variables. Algebraic propeties of the ring Int (R) of polynomials mapping a given ring R into itself are presented in the first part, starting with classical results of Polya, Ostrowski and Skolem. The second part deals with fully invariant sets of polynomial mappings F in one or several variables, for example sets X satisfying F(X)= X. This includes in particular a study of cyclic points of such mappings in the case of rings of algebrai integers. The text also contains several exercises and a list of open problems.