This dissertation examines the mechanisms that lead to the formation of actinyl peroxide cage clusters, the mechanism of aggregation of actinyl peroxide cage clusters, the photochemical generation of actinyl peroxide complexes in nonaqueous solution, and the electronic structure of the neptunyl peroxide cluster {Np24}. In order to study the formation mechanism of {U24} I have also developed spectroscopic and mass spectrometric methods to characterize these clusters in solution.  Actinyl peroxide cage clusters have been the subject of synthetic efforts by a number of groups since the single crystal structures of the first isolated clusters appeared in 2005. Herein, the mechanism by which one of these clusters, [UO2(O2)(OH)]2424- ({U24}), assembles in solution is examined in detail. Speciation data from electrospray ionization-mass spectrometry is complemented by X-ray diffraction, kinetic analyses, Raman spectroscopy, and small-angle X-ray scattering (SAXS), enabling a full description of the formation mechanism and the role of each reagent. Using this mechanistic understanding, a rational synthesis of the cluster is developed and the proposed mechanism is analyzed in terms of the structures of known uranyl peroxide cage clusters. The reactions of these cage clusters are studied in aqueous solution using similar spectroscopic and mass spectrometric methods to determine the reactivity of uranyl peroxide cage clusters and whether cluster-cluster interconversions or postsynthetic functionalization of clusters are possible. In addition, Raman and ultraviolet- visible (UV-Vis) spectroscopic analyses are used to probe the aggregation behavior of uranyl peroxide cage clusters in the presence of monovalent cations, and voltammetric and spectroscopic methods are used to study the electronic structure of the {NpO2@[Np(O2)(OH)]24} ({Np24}) cluster.  Finally, a mechanistic study describing the formation of actinyl peroxide cage clusters in nonaqueous solvents is undertaken and shown to involve the photochemical of bridging (μ2) hydroxide ligands of a dinuclear actinyl complex with concomitant evolution of dihydrogen. This reactivity is shown through a combination of isotopic labeling (2H, 18O) studies and synthetic work, and all materials are characterized by ESI-MS, UV-Vis, Raman, and nuclear magnetic resonance (NMR) spectroscopies. The evolution of dihydrogen (1H-1H and 2H-1H) is confirmed by gas chromatography-isotope ratio-mass spectrometry (GC-IR-MS) and incorporation of 18O into the peroxo ligand is monitored using the O-O symmetric stretching mode in the Raman spectrum.