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There is now ample evidence that the interstellar thick disks of spiralgalaxies are dusty. Although the majority of extraplanar gas in the first fewkiloparsecs above the plane of a spiral galaxy is matter that has been expelledfrom the thin disk, the feedback-driven expulsion does not destroy dust grainsaltogether (and there is not yet any good measure suggesting it changes thedust-to-gas mass ratio). Direct optical imaging of a majority of edge-on spiralgalaxies shows large numbers of dusty clouds populating the thick disk toheights z~2 kpc. These observations are likely revealing a cold, dense phase ofthe thick disk interstellar medium. New observations in the mid-infrared showemission from traditional grains and polycyclic aromatic hydrocarbons (PAHs) inthe thick disks of spiral galaxies. PAHs are found to have large scale heightsand to arise both in the dense dusty clouds traced through direct opticalimaging and in the diffuse ionized gas. In this contribution, we brieflysummarize these probes of dust in the thick disks of spiral galaxies. We alsoargue that not only can dust can be used to trace extraplanar material that hascome from within the thick disk, but that its absence can be a marker for newlyaccreted matter from the circumgalactic or intergalactic medium. Thus,observations of dust can perhaps provide a quantitative measure of theimportance of "outflow versus infall" in spiral galaxies.

Extraplanar Dust in Spiral Galaxies: Tracing Outflows in the Disk-Halo Interface