This year, the U.S. government is undertaking its largest peace-time operation: the decennial census. The census is an enormous logistical, technological, and social challenge that relies on a complex web of experts, community outreach, and an enormous hiring effort to conduct a complete headcount of every person living in the United States. What could possibly go wrong? The biggest challenge of an accurate census is not counting everyone. People may not be counted for a wide variety of reasons.