The paper explores why internal migration rates fell in England and Wales between 1971-81 and 2001-11. It considers all-address changing rates, short-distance migration (address changes involving moves of 10km or less) and long-distance migration (moves of 50km or more). It does so by using the Blinder-Oaxaca method to decompose the differences between the two time periods into a compositional component (changes in the aggregate migration rate attributable to increases or decreases in more or less migratory groups of the population) and a rate component – the extent to which these population groups behave differently in the two time periods. The analysis finds that changing population structure since the 1970s does not fully account for the observed decreases. Instead, it seems that changed migratory behaviour and in particular a large general downward effect that cuts across all population groups is the most important component. The greater decrease in address changing observed for all moves and those of less than 10km (compared with longer-distance moves) points the search for further explanations in the direction of factors known to be associated with short-distance moves such as the housing market and this is identified as an avenue for more research.