This paper makes the case that the era of large-scale undocumented population growth has ended, and that there is a need to reform the US legal immigration system to preserve and extend US gains in reducing undocumented entries and the US undocumented population overall. The paper demonstrates that a broad and sustained reduction in undocumented immigration to the United States occurred in the 2008 to 2015 period. It shows that the Great Recession had little, if any, role in the transformation to zero population growth of the undocumented population. Rather, the undocumented population stopped growing because of increased scrutiny of air travel after 9/11, a decade and a half of accelerating efforts to reduce illegal entries across the southern border, long-term increases in the numbers leaving the population each year, and improved economic and demographic conditions in Mexico. These conditions are likely to continue for the foreseeable future.