Abstract
Observations of seismic anisotropy provide constraints on the pattern of mantle flow and represent one of the best tools available for studying mantle dynamics. I will discuss methods for observing anisotropy in the Earth's mantle and how we interpret these observations in terms of mantle deformation. I will describe new and often surprising observations of anisotropy in key parts of the mantle, including in subduction zones and in the D" layer at the base of the mantle, and discuss the implications for our understanding of how the mantle works as a dynamic system.