This special section in the Vadose Zone Journal focusing on reactive transport modeling was developed from a special symposium jointly sponsored by the Soil Physics and Soil Chemistry Divisions of the Soil Science Society of America at the 2010 annual meetings held in Long Beach, CA. It contains eight contributions reflecting a diverse range of reactive transport modeling applications that address the fate and transport of both reactive solutes and colloidal material (i.e., viruses). Further, the eight studies range in scale from laboratory batch and column experiments to the regional scale. Three of the submissions reflect efforts to model experimental data that were already reported in the literature, providing additional insight concerning underlying physical and chemical processes. In addition to the obvious predictive applications, the eight contributions to this special section illustrate the additional advantages to including reactive transport modeling as an active component within a diverse research agenda. In addition to scenario testing, reactive transport modeling provides a framework for synthesizing diverse experimental data, evaluating the relative importance of various competing and interrelated biogeochemical processes, and identifying important data gaps and research priorities under more natural conditions at multiple temporal and spatial scales.