Dear Chimera User List Members, EMDataBank is pleased to announce the 2015/2016 Model Challenge. All members of the Scientific Community--at all levels of experience--are invited to participate as Challengers, and/or as Assessors. Benchmark targets of varying size and complexity have been selected from recently deposited 3DEM structures based on current state-of-the-art detectors and processing methods, in the resolution range 2.2-4.5 Å. Challengers are sought to create and validate models from challenge target maps in four different categories (1. optimize current cryoEM model, 2. fit known related cryoEM, crystallographic, or comparative models, 3. ab initio model building, 4. any other method of map interpretation), and upload their results with associated details. Assessors are sought to participate in evaluating submitted models. Registration is now open for all interested participants. Challengers may submit their models between November and April. Before submissions open, all are encouraged to provide feedback on submission requirements. An open assessment period will commence in late 2016. To learn more about this challenge and to register, please visit http://challenges.emdatabank.org and click on "MODEL CHALLENGE" in the menu bar. This is the second of two community-wide challenges being sponsored by EMDataBank this year to critically evaluate 3DEM methods that are coming into use, with the ultimate goal of developing validation criteria associated with every 3DEM map and map-derived model. The first challenge is focused on creating reconstructions from raw 2D image data and is currently in progress (click on "MAP CHALLENGE" in the menu bar). Sincerely, Cathy Lawson on behalf of the EMDataBank Team and the Model Challenge Committee emdatabank.org www.facebook.com/emdatabank3dem