T. Lay, Preface. Seismological Constraints on the Velocity Structure and Fate of Subducting Lithospheric Slabs: 25 Years of Progress. Introduction: Slabs and Mantle Convection. How Seismology Provides Information about Slabs. Earthquakes in Slabs. General Characterization of Slab and Wedge Structures: First-Order Slab Anomalies. Guided Waves. Wedge Structure. Thermal and Mechanical Models. Travel Time Pattern Constraints on Slab Velocity Structure:Relative Travel Time Patterns and Raytracing Analyses. Residual Sphere Modeling. Tomographical Imaging of Slab Velocity Structure. Northwest Pacific. Southwest Pacific. South America, Central America, and the Caribbean. Cascadia, Aleutians, and Alaska. Mediterranean and Hindu Kush. Slab Boundaries: Converted and Reflected Phases: Slab Seismicity and Double Benioff Zones. Constraints on Slab Boundaries and Internal Structure. Seismic Imaging of Phase Boundaries in Slabs. Focusing, Multipathing, and Diffraction Effects of Slab Structure: Short-Period Defocusing and Multipathing Effects. Long-Period Defocusing and Diffraction Effects. Future Directions in Slab Imaging. Summary. References. Subject Index.