BACKGROUND: Mexican-American fertility is poorly understood because data limitations prevent researchers from accurately estimating the fertility levels of members of this group and from determining how their fertility changes within and across generations. OBJECTIVE: Using binational data and an innovative methodological addressing key methodological limitations, I (1) estimate the fertility of Mexican Americans, (2) describe how selective Mexican migration to the United States is in terms of fertility, (3) document how Mexican-American fertility changes within and across generations, and (4) assess how educational selectivity and assimilation contribute to levels of fertility and fertility changes within and across generations. RESULTS: My findings show that migration from Mexico to the United States is positively selective with respect to fertility. Among the migrants studied, there was a disruption in fertility in anticipation of migration, but a resumption of pre-migration fertility patterns and partial compensation for the earlier fertility loss after migration. Fertility levels among Mexican-Americans appear to be decreasing within and across generations, as immigrants deviate from their pre-migration fertility patterns and increasingly adopt those of whites. Nonetheless, Mexican-American fertility has not yet fully converged with white fertility. Educational assimilation explains a considerable portion of this fertility decline within and across generations. COMMENTS: These findings highlight the importance of empirically observing the pre-migration fertility of immigrants.