This paper reviews the evidence on how poverty, environmental degradation, and gender conditions affect migration, and then tests some of the hypotheses that emerge using emigration rates from low- and middle-income countries to wealthier industrial countries. At the source country level of analysis, the relationship between income and emigration rates is non-linear. Several other variables, such as economic growth, education level, and access to health care, help to explain migration rates. While the results here must be considered preliminary, evidence does emerge that gender conditions and environmental degradation may also be associated with South-to-North migration rates.