Critical Assessment of Techniques for Protein Structure Prediction (CASP) community experiments aim to advance the state of the art in protein structure modeling. Every other year since 1994, CASP collects information on soon-to-be released experimental structures, passes on sequence data to the structure modeling community, and collects blind predictions of structure for assessment. About 100 modeling groups from around the world participate. Results of CASP experiments are published in special issues of the journal PROTEINS (e.g., CASP12: Proteins Vol 86, Issue S1, March 2018). The thirteenth CASP round is scheduled to start on May 1, 2018. The organizing committee is particularly keen to include many cryo-EM-derived structure targets in this round. The success of CASP depends on the generosity of the structure determination community. Modeling targets are needed over a wide range of difficulty, for modeling both with and without the aid of templates. Targets that can be modeled based on structural templates should ideally have 50% or less sequence identity to the templates. Access to the structure in advance of its release by the PDB or its publication is not needed. With sufficient notification to CASP (a minimum of three weeks before release, more is better) there is no need to delay structure release. If you have recently determined a novel protein structure and will be depositing it to PDB, please suggest it as a target for CASP by visiting www.predictioncenter.org/casp13/targets_submission.cgi. If you have any questions please contact [log in to unmask] CASP target providers are regularly invited to contribute to special issue papers, for example: 2018: Kryshtafovych A, Albrecht R, Baslé A, Bule P, Caputo AT, Carvalho AL, Chao KL, Diskin R, Fidelis K, Fontes CMGA, Fredslund F, Gilbert HJ, Goulding CW, Hartmann MD, Hayes CS, Herzberg O, Hill JC, Joachimiak A, Kohring GW, Koning RI, Lo Leggio L, Mangiagalli M, Michalska K, Moult J, Najmudin S, Nardini M, Nardone V, Ndeh D, Nguyen TH, Pintacuda G, Postel S, van Raaij MJ, Roversi P, Shimon A, Singh AK, Sundberg EJ, Tars K, Zitzmann N, Schwede T. (2018). Target highlights from the first post-PSI CASP experiment (CASP12, May-August 2016). Proteins 86 (S1), 27-50. doi: 10.1002/prot.25392. PMID: 2896053 2016: Kryshtafovych A, Moult J, Baslé A, Burgin A, Craig TK, Edwards RA, Fass D, Hartmann MD, Korycinski M, Lewis RJ, Lorimer D, Lupas AN, Newman J, Peat TS, Piepenbrink KH, Prahlad J, van Raaij MJ, Rohwer F, Segall AM, Seguritan V, Sundberg EJ, Singh AK, Wilson MA, Schwede T. (2016). Some of the most interesting CASP11 targets through the eyes of their authors. Proteins 84 (S1), 34-50. doi: 10.1002/prot.24942. PMID: 26473983 2014: Kryshtafovych A, Moult J, Bales P, Bazan JF, Biasini M, Burgin A, Chen C, Cochran FV, Craig TK, Das R, Fass D, Garcia-Doval C, Herzberg O, Lorimer D, Luecke H, Ma X, Nelson DC, van Raaij MJ, Rohwer F, Segall A, Seguritan V, Zeth K, Schwede T. (2014). Challenging the state-of-the-art in protein structure prediction: Highlights of experimental target structures for the 10th critical assessment of techniques for protein structure prediction experiment CASP10. Proteins 82 (S2), 26-42. doi: 10.1002/prot.24489. PMID: 2431898 2011: Kryshtafovych A, Moult J, Bartual SG, Bazan JF, Berman H, Casteel DE, Christodoulou E, Everett JK, Hausmann J, Heidebrecht T, Hills T, Hui R, Hunt JF, Seetharaman J, Joachimiak A, Kennedy MA, Kim C, Lingel A, Michalska K, Montelione GT, Otero JM, Perrakis A, Pizarro JC, van Raaij MJ, Ramelot TA, Rousseau F, Tong L, Wernimont AK, Young J, Schwede T. (2011). Target highlights in CASP9: Experimental target structures for the critical assessment of techniques for protein structure prediction. Proteins 79 (S10), 6-20. doi: 10.1002/prot.23196. PMID: 2202078 Posted on behalf of the CASP organizing committee: John Moult, University of Maryland, USA Krzysztof Fidelis, University of California, Davis, USA Andriy Kryshtafovych, University of California, Davis USA Torsten Schwede, University of Basel, Switzerland