Solid-liquid interfaces possess all of the complexities of gas-solid interfaces; yet, the presence of solvating molecules introduces specific interactions among solvent molecules, solid surfaces, and reactive species that greatly affect the efficacy of a material as a catalyst or adsorbent. These complex, manybody interactions among solvent molecules and surface species couple inherently fast electron-transfer processes with slower long-range changes in the structure of the solvation shells that cumulatively affect the free energies of adsorption, activation, and reaction. Catalytic reactions within zeolites are especially sensitive to these effects, because the pores that confine active sites possess dimensions similar to the solvation shells of surface intermediates (0.5 -2 nm). Consequently, the topology and polarity of these pores induce significant changes in the structure and dynamics of the solvent molecules. Water (H 2 O) molecules within microporous environments form intricate structures through hydrogen bonds (HB) that impact the stability of adsorbates, intrapore diffusion coefficients, and surface reactions. Decades of work have shown that HBs among aqueous solvents and polar surfaces can affect the adsorption of alcohols within microporous solids, transport of H 2 O through carbon nanotubes, and the stability of reactive surface intermediates within zeolites. The role of confined water in biocatalysis, however, is more clearly understood due to the successful characterization of water structures within the catalytic clefts of enzymes. This insight provided opportunities to design optimal solvents and mutations that improve enzymatic performance. Such knowledge does not yet exist for catalytic reactions within solvent-filled pores of zeolites despite the ubiquity and industrial importance of these systems. In zeolite catalysts, silanol defects ((SiOH) x ) and other HB donors stabilize H 2 O molecules within pores and near active sites. These H 2 O molecules form structures that depend on the topology of the zeolite and must reorganize in response to nearby catalytic events. For example, rates of 1-octene epoxidation increase 100-fold when the density of (SiOH) x increases from 0 to ~5 per unit cell within Ti-BEA, because the disruption of H 2 O clusters near Ti active sites greatly increases the entropy of the system. Conversely, glucose isomerization rates are 5 -50-fold greater in hydrophobic Ti-and Sn-BEA than hydrophilic analogues, because H 2 O co-localized near active sites forms HB structures with glucose and decreases the entropy of relevant transition states. In both of these examples, the dependence of epoxidation and glucose isomerization turnover rates on (SiOH) x density reflect changes in the thermodynamic stability of transition states via the H 2 O structures occluded within the BEA pores. Consequently, the catalysis community recognizes that H 2 O structures that form within zeolites greatly affects the stability of surface intermediates. However, we lack a quantitative understanding for how the physicochemical properties of these H 2 O structures depends on the shape and size of the surrounding pore and, more generally, how these structures impact catalysis at solid-liquid interfaces.