Family reunification is a key principle underlying U.S. immigration policy. It is embodied in the Immigration and Nationality Act (INA), which specifies numerical limits for five family-based admission categories, as well as a per-country limit on total family-based admissions. The five categories include immediate relatives of U.S. citizens and four other family-based categories that vary according to individual characteristics such as the legal status of the petitioning U.S.-based relative, and the age, family relationship, and marital status of the prospective immigrant. Of the 990,553 foreign nationals admitted to the United States in FY2013 as lawful permanent residents (LPRs), 649,763, or 66%, were admitted on the basis of family ties. Of these family-based immigrants admitted in FY2013, 68% were admitted as immediate relatives of U.S. citizens. Many of the 990,553 immigrants were initially admitted on a temporary basis and became immigrants by converting or "adjusting" their status to a lawful permanent resident. The proportion of family-based immigrants who adjusted their immigration status while residing in the United States (54%) exceeded that of family-based immigrants who had their immigration petitions processed while living abroad (46%), although such percentages varied considerably among the five family-based admission categories. Since FY2000, increasing numbers of immediate relatives of U.S. citizens have accounted for all of the growth in family-based admissions. Between FY2000 and FY2009, immigrants who accompanied or later followed principal (qualifying) immigrants averaged 12% of all family-based admissions annually. During that period, Mexico, the Philippines, China, India, and the Dominican Republic sent the most family-based immigrants to the United States. Each year, the number of foreign nationals petitioning for LPR status through family-sponsored preferences exceeds the supply of legal immigrant slots. As a result, a visa queue has accumulated of foreign nationals who qualify as immigrants under the INA but who must wait for a visa to immigrate to the United States. As such, the visa queue constitutes not a backlog of petitions to be processed but, rather, the number of persons approved for visas not yet available due to INA-specified numerical limits. As of November 1, 2013, the visa queue included 4.2 million persons. Every month, the Department of State (DOS) produces its Visa Bulletin, which lists "cut-off dates" for each of the four numerically limited family-based admissions categories. Cut-off dates indicate when petitions that are currently being processed for a numerically limited visa were initially approved. For most countries, cut-off dates range between 1.5 years and 12.5 years ago. For countries that send the most immigrants, the range expands to between 2 and 23 years ago. Interest in immigration reform has increased scrutiny of family-based immigration and revived debate over its proportion of total lawful permanent admissions. Past or current proposals for overhauling family-based admissions have been made by numerous observers, including two congressionally mandated commissions.