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This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved ; We present a comparison of 14 galaxy formation models: 12 different semi-analytical models and 2 halo-occupation distribution models for galaxy formation based upon the same cosmological simulation and merger tree information derived from it. The participating codes have proven to be very successful in their own right but they have all been calibrated independently using various observational data sets, stellar models, and merger trees. In this paper we apply them without recalibration and this leads to a wide variety of predictions for the stellar mass function, specific star formation rates, stellar-to- halo mass ratios, and the abundance of orphan galaxies. The scatter is much larger than seen in previous comparison studies primarily because the codes have been used outside of their native environment within which they are well tested and calibrated. The purpose of the `nIFTy comparison of galaxy formation models' is to bring together as many different galaxy formation modellers as possible and to investigate a common approach to model calibration. This paper provides a unified description for all participating models and presents the initial, uncalibrated comparison as a baseline for our future studies where we will develop a common calibration framework and address the extent to which that reduces the scatter in the model predictions seen here ; We further acknowledge the financial support of the 2014 University of Western Australia Research Council. MH acknowledges financial support from the European Research Council via Research Collaboration Award for 'Fast Approximate Synthetic Universes for the SKA', the ARC Centre of Excellence for All Sky Astrophysics (CAASTRO) grant number CE110001020, and the two ARC Discovery Projects DP130100117 and DP140100198 AK is supported by the Ministerio de Economía y Competitividad (MINECO) in Spain through grant AYA2012-31101 as well as the Consolider-Ingenio 2010 Programme of the Spanish Ministerio de Ciencia e Innovación (MICINN) under grant MultiDark CSD2009-00064. He also acknowledges support from the Australian Research Council (ARC) grants DP130100117 and DP140100198. He further thanks Nancy Sinatra for the last of the secret agents. PA ST/L000652/1). FJC acknowledges support from the Spanish Ministerio de Economía y Competitividad project AYA2012-39620. SAC acknowledges grants from CONICET (PIP-220), Argentina. DJC acknowledges receipt of a QEII Fellowship from the Australian Government. WC would like to acknowledge the UWA's Research Collaboration Award: PG12105017. PJE is supported by the SSimPL programme and the Sydney Institute for Astronomy (SIfA), DP130100117. FF acknowledges financial contribution from the grants PRIN MIUR 2009 'The intergalactic medium (IGM) as a probe of the growth of cosmic structures' and PRIN INAF 2010 'From the dawn of galaxy formation'. VGP acknowledges support from a European Research Council Starting Grant (DEGAS-259586). The work of BH was supported by Advanced Grant 246797 GALFORMOD from the European Research Council. MH acknowledges financial support from the European Research Council via an Advanced Grant under grant agreement no. 321323 NEOGAL. PM has been supported by an FRA2012 grant of the University of Trieste, PRIN2010-2011 (J91J12000450001) from MIUR, and Consorzio per la Fisica di Trieste. NDP was supported by BASAL PFB-06 CATA, and Fondecyt 1150300. CP acknowledges support of the Australian Research Council (ARC) through Future Fellowship FT130100041 and Discovery Project DP140100198. WC and CP acknowledge support of ARC DP130100117. AP was supported by beca FI and 2009-SGR-1398 from Generalitat de Catalunya and project AYA2012-39620 from MICINN. RAS acknowledges support from the NSF grant AST-1055081. RSS thanks the Downsbrough family for their generous support. SKY acknowledges support from the National Research Foundation of Korea (Doyak 2014003730)