In June 2012 President Obama signed an executive order establishing the Deferred Action for Childhood Arrivals (DACA) program. The President acted because the U.S. Congress had repeatedly failed to pass the "Dream Act" - legislation protecting from deportation young undocumented immigrants who had been brought to the United States as children. More than 818,000 "Dreamers" applied for protection under the President's program through September 2014. They received short-term relief from deportation, not permanent legal status.This volume is the first scholarly attempt to comprehensively address the question of why some age-eligible immigrants have applied for DACA status while many more - nearly two-thirds of those estimated to be potentially eligible - have not. The study devotes special attention to the geography of DACA -- how place of residence influences the likelihood of participation -- and the role of social networks in transmitting knowledge about the program. Qualitative interviews illuminate life after receiving DACA status. The interviewees report that DACA status has positively transformed their lives, especially in terms of educational and economic advancement. However, as a consequence of their tentative legal status, they continue to face significant limits and obstacles to full incorporation into the United States. They are eager to translate their three-year deferral of deportation into legal permanent residency, but Congress has not provided a path for doing so, and Obama's executive action can be reversed by a future President. The authors draw upon five different types of data collected for the study, including a large-scale, on-line survey of undocumented millenials; a national-level dataset on DACA applicants; survey interviews with residents of a high-emigration community in Oaxaca, Mexico and a random sample of Mexican-born persons now living in San Diego County; and in-depth, semi-structured interview with undocumented youths in San Diego County who had applied for DACA. They propose fourteen policy recommendations, for increasing future participation in the DACA program and for enhancing the economic, social, and psychological integration of those who benefit from it.