  Using data from the WISE all-sky survey we discovered that the non-thermal
infrared (IR) emission of blazars, the largest known population of
extragalactic gamma-ray sources, has peculiar spectral properties. In this
work, we confirm and strengthen our previous analyses using the latest
available releases of both the WISE and the Fermi source catalogs. We also show
that there is a tight correlation between the mid-IR colors and the gamma-ray
spectral index of Fermi blazars. We name this correlation "the
infrared--gamma-ray connection". We discuss how this connection links both the
emitted powers and the spectral shapes of particles accelerated in jets arising
from blazars over ten decades in energy. Based on this evidence, we argue that
the infrared--gamma-ray connection is stronger than the well known
radio--gamma-ray connection.
