Abstract: A Kleene's Theory of Real Valued Functions We explain from very basic notions how a theory of recursive real valued functions can be developed. Besides its mathematical contents, we foresee many interesting applications either in the theory of dynamical systems either in classical computability and complexity theories. Many aspects of this research have been presented in several conferences and workshops, but the very crucial notions, e.g. of iteration, of simulation of Turing machines by differential equations, of representation of classical complexity classes, of relations with hyperarithmetical and analytical hierarchies are somewhat not known to a reasonable percentage of computer scientists, not to say almost all. It is our main motivation to show how elegant this theory can get, how fruitful and how simple it can be made (with first conceps of mathematics). +++++++++++++++++++++++++++++++++++++++++++++++ J. Felix Costa Departamento de Matematica Instituto Superior Tecnico Av. Rovisco Pais, 1049-001 Lisboa, PORTUGAL tel: 351 - 21 - 841 71 45 fax: 351 - 21 - 841 75 98 e-mail: fgc@math.ist.utl.pt www: http://fgc.math.ist.utl.pt/jfc.htm +++++++++++++++++++++++++++++++++++++++++++++++