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tokens: blazar-like counterparts of the UGSs. 3. We describe the statistically significant correlations between the γ -ray photon index and the mid-IR colors for both the whole sample of Fermi blazars and the BZB and BZQ spectral classes separately, the basis of the IR– γ -ray connection. This correlation appears “stronger” than the well-known radio– γ -ray connection because it involves the spectral shapes of the Fermi blazars over ∼10 orders of magnitude and not only their fluxes. 4. We argue that the peculiar mid-IR colors of Fermi blazars do not depend on their γ -ray photon index. In turn, the IR– γ -ray connection is unexpected. We have also highlighted its potential use to implement the search for blazar-like counterparts of the Fermi UGSs. 5. We show that a large fraction of the BCUs listed in the 3FGL whose WISE counterpart has mid-IR colors consistent with the WISE Gamma-ray Strip have Fermi spectral index values consistent with the IR– γ -ray connection. Taking advantage of the overwhelming fraction of Fermi blazars detected in the WISE all-sky survey (i.e., ∼99%) in the first two mid-IR filters, we suggest that a comprehensive investigation of their IR properties at the light of the IR– γ -ray connection described in this paper can represent a powerful tool to reveal the real fraction of Fermi blazars hidden within the sample of UGSs. We thank the anonymous referee for useful comments that led to improvements in the paper. We also thank J. Ballet for helpful discussions. F.M. gratefully acknowledges the financial support of the Programma Giovani Ricercatori—Rita Levi Montalcini—Rientro dei Cervelli (2012) awarded by the Italian Ministry of Education, Universities and Research (MIUR). This research has made use of data obtained from the high-energy Astrophysics Science Archive Research Center (HEASARC) provided by NASA’s Goddard Space Flight Center. The NASA/IPAC Extragalactic Database (NED) is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Part of this work is based on the NVSS (NRAO VLA Sky Survey). The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under contract with the National Science Foundation and on the VLA Low-frequency Sky Survey (VLSS). The Molonglo Observatory site manager, Duncan Campbell-Wilson, and the staff, Jeff Webb, Michael White, and John Barry, are responsible for the smooth operation of the Molonglo Observatory Synthesis Telescope (MOST) and the day-to-day observing program of SUMSS. SUMSS is dedicated to Michael Large, whose expertise and vision made the project possible. The MOST is operated by the School of Physics with the support of the Australian Research Council and the Science Foundation for Physics within the University of Sydney. This publication makes use of data products from the Wide-field Infrared Survey Explorer , which is a joint project of the University