Environmental archives, such as sediments, banded corals and tree rings, are widely used to reconstruct past environmental conditions of ecosystems. In particular, 210 Pb has been used during more than 4 decades, through dating of undisturbed sediment cores, to study ecosystem changes during the last 100yr. Since its inception, diverse dating models have been proposed, developed, used and validated in numerous environments, but their nomenclature and formulation is not homogenous. In this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation, which relates excess 210 Pb concentration in sediment, its flux to the sediment surface and mass accumulation rate. From this equation, models were consistently named based on the main hypothesis used and, using a unified and logical nomenclature, dating equations were derived in detail. We applied in detail most of the described models to a sediment core from Mexico and uncertainty expressions were also included. Finally, some recommendations to use the models are proposed. We believe that this work can facilitate the use of 210 Pb as a tool to date sediment cores in a more homogeneous way. © 2011 Elsevier Ltd.