In October 2011 an American Geophysical Union Chapman Conference was held in Grindelwald, Switzerland, titled “Advances in Lagrangian Modeling of the Atmosphere.” Lagrangian models are being applied to a wide range of high-impact atmospheric phenomena, such as the transport of volcanic ash and dispersion of radioactive releases. One common theme that arose during the meeting is the need for improved access to the output products of forecast models and reanalysis systems, which are used as in-puts to trajectory and dispersion models. The steady increases in horizontal and vertical resolution in forecast models and data assimilation systems have not been accompanied by changes in model output products, such as higher-frequency winds and the provision of important auxiliary parameters (e.g., heating rates and subgrid-scale mixing properties). This paper discusses the principles of Lagrangian kinematic models and recommends changes in model output practices that would lead directly to significant improvements in the accuracy of trajectory and dispersion calculations.