  The active galactic nucleus (AGN) phenomena results from a supermassive black
hole accreting its surrounding gaseous and dusty material. The infrared (IR)
regime provides most of the information to characterize the dusty structures
that bridge from the galaxy to the black hole, providing clues to the black
hole growth and host galaxy evolution. Over the past several decades, with the
commissioning of various ground, airborne and space IR observing facilities,
our interpretations of the AGN circumnuclear structures have advanced
significantly through improved understanding of how their dust emission changes
as a function of wavelength and how the heating of the dusty structures
responds to variations of the energy released from the central engine. In this
review, we summarize the current observational knowledge of the AGN IR
broad-band spectral energy distributions (SEDs) and the IR time variability
behavior covering large ranges of AGN luminosity and redshift, and discuss some
first-order insights into the obscuring structures and host galaxy IR
properties that can be obtained by integrating the relevant observations into a
coherent picture.
