An analysis of the complexity involved in the computational modeling of catalytic reactions is presented, including a review of applications and limitations of ab. initio methods in this context. The foundations of parametric methods based on simulation techniques and the use of elementary parametric energy functionals are briefly discussed. We describe the implementation and facilities of a quantum-chemical package, usually referred to as CATIVIC, especially tailored for catalytic processes. Finally, the application of this code to catalytic systems is illustrated with several examples. (C) 2004 Published by Elsevier B.V.