A complex tracking system, the National Income and Product Accounts (NIPA) is used to measure and monitor the U.S. economy. This article surveys the main data sources currently used in the NIPA. It is not primarily an article about methodology, but focuses instead on the raw inputs to the process: Who is answering what kinds of questions? Closer acquaintance with the data sources behind the accounts highlights the considerable uncertainty about exact magnitudes of various aggregate quantities (and their growth rates) and the need for ongoing evaluation of the data-collection efforts that support the accounts.