The energetics of water incorporation and proton–dopant association in ZrO₂ grain boundaries, namely Σ 5(310)/[001] and Σ 5(210)/[001], are calculated using atomistic simulation techniques and are compared to results obtained for the cubic bulk material. The interatomic potential set was chosen from those available in the literature on the basis of the best fit to experimental data. Both the calculated hydration energy and the redox reaction energies for cubic bulk ZrO₂ are shown to be high, in agreement with the experiment. In contrast, the hydration energies for oxygen ions in and around the grain boundaries are far lower, while the redox energies are also significantly reduced. Strong binding energies between acceptor dopants and protons in bulk ZrO₂ suggest significant proton trapping. While binding (proton trapping) is still prevalent in the grain boundary structures, the binding energies are generally smaller suggesting that should proton conduction occur it is most likely to occur along the grain boundaries rather than the bulk material. Binding is found to be the strongest for smaller ions like Sc and weaker for larger ions like Gd and La. Comparisons between the results for the two grain boundary structures are also made and the consequences for proton migration are assessed.