Subducting oceanic lithosphere is a key engine of mass exchange on Earth, with major petrological, geochemical, and geodynamic consequences at the surface and at depth. We welcome contributions that shed light on the nature of the slab in space and time, from outboard of the trench to past the arc front, from mass gain to mass loss, from the Archean to today. Perspectives gleaned from experimental petrology, numerical modeling, and observations of slabs (drill cores, xenoliths, exhumed terranes) will all contribute to a more synthetic picture of how slabs evolve in space and time.