Migration flows around the U.S. have shown a great deal of temporal and geographical differentiation over the past few decades. However, the recent downturn in the U.S. economy provides a renewed motivation to explore the relationship between the macro-economy and interstate migration. To address this issue, in this paper patterns of interstate migration are analyzed using IRS data and several migration efficiency measures for 18 2-year time periods, 1988–2006. Included in the analysis is an examination of the relationship between system migration and economic change, structural changes in the migration system over time (national and state level), and changes in the geography of state-level migration efficiency rates. As might be expected, the two full business cycles that occurred over this time period saw significant short-term changes in migration flows, although the economic downturn of 2001-02 may indicate more fundamental changes in the migration system.