  We review the nearby debris disk structures revealed by multi-wavelength
images from Spitzer and Herschel, and complemented with detailed spectral
energy distribution modeling. Similar to the definition of habitable zones
around stars, debris disk structures should be identified and characterized in
terms of dust temperatures rather than physical distances so that the heating
power of different spectral type of stars is taken into account and common
features in disks can be discussed and compared directly. Common features, such
as warm (~150 K) dust belts near the water-ice line and cold (~50 K)
Kuiper-belt analogs, give rise to our emerging understanding of the levels of
order in debris disk structures and illuminate various processes about the
formation and evolution of exoplanetary systems. In light of the disk
structures in the debris disk twins (Vega and Fomalhaut), and the current
limits on the masses of planetary objects, we suggest that the large gap
between the warm and cold dust belts is the best signpost for multiple
(low-mass) planets beyond the water-ice line.
