ACT-America, or Atmospheric Carbon and Transport – America, will conduct five airborne campaigns across three regions in the eastern United States to study the transport and fluxes of atmospheric carbon dioxide and methane. Each 6-week campaign will measure how weather systems transport these greenhouse gases. The objective of the study is to enable more accurate and precise estimates of the sources and sinks of these gases. Better estimates of greenhouse gas sources and sinks are needed for climate management and for prediction of future climate. ACT America addresses three primary sources of uncertainty in our ability to infer carbon dioxide and methane sources and sinks - transport error, prior flux uncertainty and limited data density.