Three competing defect configurations of Li-doping of MgO on the (100), (110) and (111) low index surfaces have been investigated using GGA + U. The three configurations investigated on each of the surfaces were: substitution of Li for Mg with the formation of a compensating oxygen hole state ([Li'Mg—O•O]), substitution of Li for Mg with the addition of a Li surface interstitial ([Li'MgLi•i]) and the clustering of two Li ions with the formation of a neutral [Li'MgV••OLi'Mg] oxygen vacancy. The electronic structure, geometry and energetics of these defects are examined, and the effect on catalytic activity is discussed. Hydrogen abstraction from methane on the three surfaces is also investigated. Our results demonstrate that the energetics associated with hydrogen adsorption are strongly surface dependent, with the (111) oxygen terminated surface indicated as being the most promising catalytically.