Between 1900 and 1918 the Labour party changed from being a new organization operating on the fringes of the Liberal party, to being the largest British opposition party. This change has attracted a great deal of historical attention. The analysis of electoral results in general, and municipal election results in particular, rightly plays a major part in the conflicting explanations of why this realignment took place. Negatively, this paper seeks to establish that many of the methods of examining electoral material common in the literature are in fact inadequate. It is also suggested, more positively, that despite problems with the way results are currently used, even a modestly elaborated treatment of municipal election results can reveal significant information about the origins and location of Labour's support. Accurate ‘quantification’ cannot of itself explain the rise of Labour, or the pattern of electoral politics more generally. It can, however, be an important component of broader attempts at establishing why political changes took place both in Edwardian Britain and in the still under-researched period between 1918 and 1931.