Conventional analyses of local government structure focus on the revolutionary changes that result from deliberate reorganisations. We propose a new perspective on structural change that emphasises the importance of evolutionary processes as well as radical reforms. Evolutionary changes in structure are caused, for example, by population growth or decline and reallocations of service responsibilities between tiers. The argument is illustrated by an empirical analysis of fragmentation and concentration in the structure of local government in London. The evidence reveals that structural change is the norm rather than the exception: it occurs even when the absolute number of local government tiers and units is constant.