The application of SE estimation methods for small enclosures is the main subject of this thesis. Three Shielding Effectiveness estimation methods are presented; Empirical, Experimental and Numerical Simulation. SE estimates have been compared with SE measurements showing close correlations between the numerical simulation and the experimental results. It has been proved that the SE of an empty enclosure, compared with that of an enclosure containing a printed circuit board, differs due to volume change, herein Q variation. Conclusions are formulated in terms of further works to be accomplished in order to determine better measurement and simulation models for Shielding Effectiveness estimates.