Several recent studies, which have used 3-D seismic tomography to separately illuminate the crust and upper mantle have yielded valuable constraints on seismic properties in the lithosphere. The two primary techniques have been teleseismic tomography, which exploits relative arrival times from distant earthquakes to image the upper mantle, and ambient noise tomography, which makes use of diffuse energy produced by oceanic microseisms and atmospheric disturbances to image crustal structure.