Metal-organic frameworks (MOFs) are 3-dimensional (3D) inorganic-organic hybrid materials. Due to their hybrid structures, MOFs have been increasingly become attractive materials for energy related applications. In recent years, many methods have been investigated and utilized to functionalize MOFs with a variety of chemical groups to enhance its properties. Among these methods, prefunctionalization and postsynthetic modification methods (PSM) have been proven to be versatile and accessible pathways to incorporate functional groups into MOFs. In this dissertation, the use of prefunctionalization and PSM methods to decorate MOFs with functionalities, and an overview of functionalized MOFs for applications in gas storage and catalysis will be highlighted and investigated. In the first part of the dissertation, a series of free phenylpyridine functionalized MOFs are synthesized and characterized. These MOFs are further decorated with Ir(I) and Rh(I) via cyclometalation reactions using PSM method. Amazingly, a selective PSM on an interpenetrated MOF is unprecedentedly observed. The selective outcome of the PSM is the result of the spatial difference between of chemically modifiable sites within the interpenetrated framework. In the second haft of this dissertation, Ir(I)phenylpyrdine functionalized MOFs are showed to be effective, stable, and reusable heterogeneous catalysts for allylic N-alkylation of amines. Furthermore, the use of prefunctionalization and PSM methods are utilized for the rational synthesis of a bifunctional, site-isolated MOF that has both organocatalytic -NH2 and organometallic Ir(I)phenylpyridine. The bifunctional MOF is further investigated as a tandem catalyst for one-pot condensation and alkylation reactions. Lastly, the synthesis of the first pair of isomeric MOFs is realized via prefunctionalization and PSM methods. More importantly, these cubic isoreticular MOFs with disordered ordered phenyl amide substituents displayed drastic differences in their sorption toward both N2 and H2. This observed differences suggest a new strategy to modulate H2 sorption of MOFs and to potentially produce MOFs with ideal behaviors for application in H2 storage.