The state‐of‐the‐art knowledge of atmospheric organic constituents in the lower troposphere has been compiled in order to reconcile sources, transport processes, fates, and relative contributions of natural background organic vs. anthropogenic organic emissions. Volatile compounds and residual particulate organic carbon are the dominant fractions in both urban and remote areas. The lipid fractions have highest concentrations in urban centers, intermediate concentrations in rural areas, and lowest over the oceans. The same distribution is found for residual organic carbon and total vapor phase organic carbon. This large burden of urban contamination is attributed to residues from incomplete combustion of fossil fuels and industrial processes. Comparisons of homologous‐series, molecular markers, and bulk properties of macromolecular organic matter are used for the chemical speciation of organic aerosols. The instrumental methods of analyses described are all in use for a variety of analytical purposes including atmospheric organic matter. A general discussion of sampling methods for various molecular weight regimes of organic aerosols is also presented.