The main theme of this dissertation concerns the study of the properties of zeolites and modified zeolites with respect to reactivity and catalysis by way of MAS NMR and theoretical modeling with Density Functional Theory(DFT). The combined use of MAS NMR and DFT to study zeolites and their interactions with adsorbed species has provided a synergy resulting from the detail provided by theoretical modeling of zeolite cluster models vetted through comparison to experimentally available observables. This tandem mode of examining problems related to zeolite characterization has been facilitated by the increase in computational power where models containing larger numbers of atoms and very large basis sets can now be routinely employed.; The first two chapters of this dissertation pertain to the general study of zeolite acidity, its measurement and impact on adsorabate interactions and thecalculation of various NMR parameters such as quadrupole coupling constants, chemical shifts and Spin-Spin coupling constants. The remaining two chapters expand on the basic concepts of the earlier chapters by studying a Rhodium based zeolite catalyst and its catalytic activity with respect to ligand exchange and acetylene cyclotrimerization. The excellent agreement between the analytical techniques applied in these two chapters demonstrates the power in combining spectroscopy with theoretical methods for the elucidation of more complex reactions.