Compared with other demographic processes, remarkably little attention has been given to the way internal migration varies between countries around the world. We set out the rationale for such comparisons and identify the impediments which have constrained prior work, including a global review of the types of migration data collected. We then draw upon an extensive repository of data assembled through the IMAGE (Internal Migration Around the Globe) project to compare countries with respect to the overall intensity of migration over one- and five-year intervals, the age profile of migration, and the spatial patterns of population movement. We identify marked variations both between and within world regions on each of these dimensions, and document a general decline in mobility over the period 1990-2000. Analysis reveals close links between migration and some aspects of national development but also underlines the significance of history, culture, and social context in shaping mobility behavior. We stress the need for greater harmonization of national practice in collection of internal migration data in order to enhance cross-national comparisons.