This article examines the relative importance of de novo entry, population migration, and multibank holding company activity in explaining concentration changes in Wisconsin during the 1970s. Perhaps better than any other state in the Seventh District, Wisconsin offers a glimpse of future structural developments in banking. First, the state has a mature bank holding company movement dating back to the turn of the century and is more likely to exhibit the long-run effects of that movement than a state like Michigan, which has permitted multibank holding companies only since 1971. With legislative proposals to permit multibank holding companies being introduced each year in Illinois and Indiana, this experience could be extremely useful in judging the effects of those proposals. Second, because Wisconsin has allowed limited branching since 1968 (after prohibiting the establishment of new branches between 1947 and 1968), its banking structure should also reflect the effects of branching on concentration.