Why has Mexican migration to the United States plummeted to levels not seen since the early 1970s? Most analysts have blamed the Great Recession of 2007-2009 in the United States. But why have new departures for the United States failed to rebound to pre-Recession levels, more than six years into the recovery? Beyond the perception that jobs are hard to come by in the United States, what other factors may be influencing so many Mexicans to forego going north? Has a new calculus of staying home in Mexico taken hold in previously high-emigration communities? To answer these and other questions, the Mexican Migration Field Research and Training Program (MMFRP) at the University of California-San Diego returned to Tunkas, a town in central Yucatan that has sent migrants to the United States since the 1970s. This volume reports results from the MMFRP's fourth study of Tunkasenos in Yucatan and the southern California cities where most of the town's migrants have clustered. Drawing on 558 survey interviews and 87 open-ended interviews conducted in the first quarter of 2015, the authors show how the migration behavior of Tunkasenos has changed in recent years, and they test seven hypotheses to explain the change. Among other explanations, the increased attractiveness of internal migration to Mexican cities has reduced the pool of potential migrants to the United States. This volume also presents results from the MMFRP's most exhaustive study to date of factors influencing educational attainment among young Tunkasenos on both sides of the border. The authors find that while Tunkasenos are completing more years of education than ever before, significant obstacles to educational advancement continue to operate. They call special attention to rising drug and alcohol use among adolescents in Tunkas, and find that having a parent absent due to migration is an important risk factor. Drawing on extensive qualitative evidence, the following chapter explores the U.S. side of the equation, focusing on risk factors for drug and alcohol use among California-based migrants from Tunkas. The authors find that pressures generated by their U.S. work life and social networks formed after arrival in the United States increase migrants' vulnerability to substance use. The final chapter is a path-breaking analysis of how global climate change is affecting the livelihoods and migration behavior of Tunkasenos."