The U.S. Constitution—Article 1, Section 2, clause 3, as modified by Section 2 of the Fourteenth Amendment—requires a population census every 10 years, to serve as the basis for apportioning seats in the House of Representatives. Decennial census data also are used for within-state redistricting and in certain formulas that determine the annual distribution of more than $450 billion in federal funds to states and localities. Census numbers, moreover, are the foundation for constructing national and state estimates of current population size and projections of future size. The Constitution stipulates that the enumeration is to be conducted "in such Manner as they [Congress] shall by Law direct." Congress, through Title 13 of the United States Code , has delegated this responsibility to the Secretary of Commerce and, within the Department of Commerce (DOC), the Census Bureau. Both the Commerce Secretary and the Census Bureau Director are appointed by the President, by and with the advice and consent of the Senate. The Census Bureau's task in conducting the once-a-decade enumeration has been summarized very simply: count each person whose usual residence is in the United States; count that person only once; and count him or her at the right location, where the person lives all or most of the time. Far from being simple, however, the attempt to find and correctly enumerate 100% of U.S. residents is increasingly complicated and expensive, even though Title 13 U.S.C., Section 221, requires compliance with the census and provides for a fine of up to $100 for nonresponse. In accordance with provisions of the Sentencing Reform Act of 1984, Title 18 U.S.C., Sections 3559 and 3571, the possible fine has been adjusted to not more than $5,000. This report discusses the major innovations that were planned for the 2010 census, problems encountered with the attempt to automate certain census field operations, the persistent differential census undercount of less advantaged groups in the population, and efforts to ensure an equitable census. Table 1 shows the completion of key census activities; the production and release of 2010 census products continued through 2013. The 23 rd census began north of the Arctic Circle on January 25, 2010, in Noorvik, AK, where the then-Bureau Director, among others, traveled by snowmobile and dogsled to enumerate the residents. Most U.S. households—about 120 million—received their census forms by mail in March, ahead of the official April 1 Census Day, and 74% of the households that received forms mailed them back. From May through July, about 565,000 census takers contacted approximately 47 million households that either did not receive a questionnaire or did not answer and return it. On December 21, 2010, 10 days before the legal deadline, the Bureau released the official state population figures for House apportionment and the total U.S. resident population count of 308,745,538 as of Census Day. A brief overview of modern census-taking shows how the Bureau has collected the decennial data from 1940 onward. In that year, for the first time, the census questionnaire contained 16 supplementary questions asked of a 5% sample of the population. Sampling continued to be done in conjunction with the 1950 through 2000 censuses, and in 1970 the census became primarily a mail-out, mail-back operation. In 2000, for example, the Bureau sent a set of basic questions on a short form to most housing units; a sample of units—about 17%—received a long form containing these questions and others designed to gather socioeconomic and housing data for various legislative and program purposes. The forms were delivered to housing units on the Bureau's address list, with instructions that respondents were to complete and return them. Departing from recent enumerations, the 2010 census questionnaire was a short form only. It asked for the age, sex, race, and ethnicity (Hispanic or non-Hispanic) of each person in a household, as well as the individual's relationship to the person filling out the form. The form also included a question about tenure, that is, whether the housing unit was rented or owned by a member of the household. The long form was replaced by the American Community Survey (ACS), a "continuous measurement" survey of, from 2005 to 2011, about 250,000 households per month, totaling about 3 million annually (now about 295,000 households per month, totaling about 3.54 million a year), which, with few exceptions, gathers the same data as its predecessor. The Bureau highlights the more timely availability of information as a key benefit of the ACS. It provides annual data for areas with populations of at least 65,000 people, including the total United States, all states and the District of Columbia, all congressional districts, about 800 counties, and about 500 metropolitan and micropolitan statistical areas. For less populous areas, the Bureau produces multi-year estimates based on ACS data collected over several years. In 2008, the Bureau released the first three-year estimates for areas with 20,000 or more people, and on December 14, 2010, the first five-year estimates became available for areas from the most populous to those with fewer than 20,000 people. Another innovation for 2010 was to have been the automation of two major census field operations: address canvassing and nonresponse follow-up (NRFU). The goal of pre-census address canvassing was for temporary Bureau field staff to verify and correct census addresses and maps, technically called the "Master Address File" (MAF) and "Topologically Integrated Geographic Encoding and Referencing" (TIGER) system. An accurate MAF/TIGER was essential for directing the census forms to the right housing units and successfully conducting nonresponse follow-up. Indeed, as the Bureau has noted, "MAF/TIGER is the foundation of the Census—it creates the universe for all other operations that collect information from the public." NRFU required that enumerators try repeatedly to visit or telephone people who had not completed their census questionnaires and convince them to respond. Because of the problems discussed below, only address canvassing was automated; NRFU was not. As part of its 2010 census preparations, the Bureau contracted with the Harris Corporation for Field Data Collection Automation (FDCA). The objective was the development of highly specialized handheld computers to automate address canvassing and update maps with global positioning software, as well as conduct nonresponse follow-up. Testing eventually revealed significant flaws in the handhelds, such as slow operation, memory problems, and a tendency to lock up when users entered large quantities of data. In April 3, 2008, congressional testimony, then-Bureau Director Steve Murdock acknowledged that the Bureau had abandoned the plan to use the handhelds for NRFU, would resort to the traditional paper-based approach, and would rely on the handhelds only for address canvassing. The change required the Bureau to hire and train more NRFU staff, at increased expense. The Government Accountability Office (GAO) testified to Congress on June 11, 2008, that the Bureau had re-estimated the total life-cycle cost of the 2010 census at between $13.7 billion and $14.5 billion, instead of the previously estimated $11.5 billion. A 2009 House Committee on Appropriations report raised the estimate to $14.7 billion, where it remained in March 2010. NRFU was expected to account for about $2.3 billion of the $14.7 billion. On November 18, 2008, the Commerce Department's Office of Inspector General (OIG) issued a report that identified the top management challenges DOC faced as it prepared for the transition to a new President and new Commerce Secretary. Heading the list was the need to "overcome the setbacks experienced in reengineering decennial processes and conduct a successful 2010 Census." The failure of the handhelds was prominent among the setbacks noted. According to the report, the Bureau "originally intended to develop the handhelds in-house and tested prototypes in ... 2004 and 2006. The devices had serious problems in both tests," which, in the OIG's view, "should have better informed the Bureau's efforts to define requirements." The decision to contract for FDCA came "too late in the decade ... to meet ambitious fixed deadlines for the dress rehearsal tests starting in 2007 and decennial operations starting in 2009." Not until January 2008, almost two years after awarding the contract, did the Bureau deliver "a first draft of a complete, user-validated set of requirements for the handhelds and supporting infrastructure." By then, the MITRE Corporation, which periodically advised the Bureau about its information technology (IT) programs for the 2010 census, had found that FDCA is in serious trouble. It is not clear the system will meet Census' operational needs and quality goals. The final cost is unpredictable. Immediate, significant changes are required to rescue the program. However, the risks are so large considering the available time that we recommend immediate development of contingency plans to revert to paper operations. The OIG report acknowledged that the Bureau had taken important actions, such as management changes and better oversight, to address these problems, but stated that "significant risks remain for the 2010 decennial." Similarly, the Government Accountability Office pointed out vulnerabilities in the Bureau's management of its information technology systems, including the handheld computers. In a November 6, 2008, press release to announce its presidential transition website, GAO included the upcoming census among its 13 "urgent issues ... needing the attention of [then-] President-Elect Obama and the 111 th Congress during the transition and the first year of the new administration and Congress." The 2010 census, in large part because of IT problems and a substantial total estimated cost, remained one of the areas GAO designated as "high risk" in a January 2009 update of its high-risk series.