Using a series of graphs, the authors analyse the general characteristics of the evolution of the population of 1596 municipalities in Québec for two successive ten year periods (1951-61 and 1961-71) and for the entire twenty year period (1951-71). An initial set of graphs, consisting of histograms, reveal the relative frequency of recurrence of various degrees of positive and negative population change. A second set illustrates the characteristics of the evolution of the municipalities in terms of their number and population by size class. The concentration of the population is then analyzed by means of Lorentz curves. Finally, the characteristics of the demographic evolution by type of change, negative or positive, are examined. This research reveals that over the twenty year period 1951-71 the population of Québec has become more and more concentrated in an ever decreasinq number of municipalities, especially those having population between 20 000 and 100 000. By contrast, the number of municipalities suffering population losses has increased, but represents an ever decreasing proportion of the total population of Québec. It is the small rural municipalities (2 000 people or less) which have suffered the most serious losses. The work thus considers the process of urbanisation with respect to the size structure of the municipalities of Québec.