Modern market economies are probably the most complex institutions ever devised by human beings. In the United States, by far the most complex of these tracking systems is the National Income and Product Accounts (NIPA). This article's objective is to survey 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.