The biogeochemical cycling of carbon, water, energy, aerosols, and trace gases in the Amazon Basin was investigated in the project European Studies on Trace Gases and Atmospheric Chemistry as a Contribution to the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA‐EUSTACH). We present an overview of the design of the project, the measurement sites and methods, and the meteorological conditions during the experiment. The main results from LBA‐EUSTACH are: Eddy correlation studies in three regions of the Amazon Basin consistently show a large net carbon sink in the undisturbed rain forest. Nitrogen emitted by forest soils is subject to chemical cycling within the canopy space, which results in re‐uptake of a large fraction of soil‐derived NOx by the vegetation. The forest vegetation is both a sink and a source of volatile organic compounds, with net deposition being particularly important for partially oxidized organics. Concentrations of aerosol and cloud condensation nuclei (CCN) are highly seasonal, with a pronounced maximum in the dry (burning) season. High CCN concentrations from biomass burning have a pronounced impact on cloud microphysics, rainfall production mechanisms, and probably on large‐scale climate dynamics.