The structure and properties of methylaluminoxane (MAO) continue to attract interest in the context of olefin polymerization using metallocene or other single-site catalysts. Recent attention has been focused on the synthesis and structure of modified MAO and solid MAO, which are typically prepared using non-hydrolytic methods. The identity of the reactive components of hydrolytic MAO, prepared via the controlled hydrolysis of Me3Al, remained largely unknown. This mystery, however, was partly solved by the recent isolation and characterization of a reactive sheet structure, (MeAlO)26(Me3Al)9 (hereinafter "26,9"), by Luo et al. Theory suggests the bulk of hydrolytic MAO contains relatively unreactive large cages, or other structures, with tetrahedral O3AlMe and trigonal O groups in six-membered or larger (MeAlO)n rings. Reactive structures consist of strained cages, especially those with vicinal (MeAlO)2 rings, extended cages or nanotubes with reactive groups formed via the addition of structural Me3Al to the vertices and ends of these structures, and two-dimensional sheets analogous to 26,9 with reactive sites incorporating structural Me3Al along their edges.