1 The ODD protocol: a review and first update 1 Volker Grimm 1 , Uta Berger 2 , Donald L. DeAngelis 3 , J. Gary Polhill 4 , Jarl Giske 5 , Steven F. Railsback 6 1 UFZ, Helmholtz Centre for Environmental Research – UFZ, Department of Ecological Modelling, Permoserstr. 15, 04318 Leipzig, Germany (volker.grimm@ufz.de ) 2 Institute of Forest Growth and Computer Science, Dresden University of Technology, P.O. 1117, 01735 Tharandt, Germany 3 USGS/Biological Resources Division and Dept. of Biology, University of Miami, PO Box 249118, Coral Gables, FL 33124, USA 4 Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH, United Kingdom. 5 University of Bergen, Department of Biology, P. O. Box 7803, N-5020 Bergen, Norway 6 Department of Mathematics, Humboldt State University; and Lang, Railsback & Associates, 250 California Avenue, Arcata, California 95521, USA Abstract The ‘ODD’ (Overview, Design concepts, and Details) protocol was published in 2006 to standardize the published descriptions of individual-based and agent-based models (ABMs). The primary objectives of ODD are to make model descriptions more understandable and complete, thereby making ABMs less subject to criticism for being irreproducible. We have systematically evaluated existing uses of the ODD protocol and identified, as expected, parts of ODD needing improvement and clarification. Accordingly, we revise the definition of ODD to clarify aspects of the original version and thereby facilitate future standardization of ABM descriptions. We discuss frequently raised critiques in ODD but also two emerging, and unanticipated, benefits: ODD improves the rigorous formulation of models and helps make the theoretical foundations of large models more visible. Although the protocol was designed for ABMs, it can help with documenting any large, complex model, alleviating some general objections against such models. Keywords: model description, model formulation, model replication, scientific communication, standardization August, 2010 1 To appear in Ecological Modelling.