This article investigates the solvability of volume integral equations arising in elastodynamic scattering by penetrable obstacles. The elasticity tensor and mass density are allowed to be smoothly heterogeneous inside the obstacle and may be discontinuous across the background-obstacle interface, the background elastic material being homogeneous. Both materials may be anisotropic, within certainme limitations for the background medium. The volume integral equation associated with this problem is first derived, relying on known properties of the background fundamental tensor. To avoid difficulties associated with existing radiation conditions for anisotropic elastic media, we also propose a definition of the radiating character of transmission solutions. The unique solvability of the volume integral equation (and of the scattering problem) is established. For the important special case of isotropic background properties, our definition of a radiating solution is found to be equivalent to the Sommerfeld-Kupradze radiation conditions. Moreover, solvability for anisotropic elastostatics, directly related to known results on the equivalent inclusion method, is recovered as a by-product. 1. Introduction. Volume integral equations, also known as Lippmann-Schwinger integral equations, arise naturally when considering the scattering of waves by penetrable inhomogeneities embedded in a homogeneous background medium, for which a fundamental solution is known. They have been developed and used in various areas of physics such as electromagnetism and optics [3, Chap. 2] [8, Chap. 9], acoustics [28] [9, Chap. 8], or elastodynamics [34, 35, 39], since a long time. If the penetrable object has homogeneous properties, scattering may alternatively be modelled using coupled surface integral equations, see e.g. [13] for elastodynamics. Variational formulations, combined with appropriate handling of the solution behavior at infinity, can also be applied to such scattering problems.Volume integral equations have a geometrical support restricted to the spatial region where material properties differ from the background. This feature makes them useful e.g. for deriving asymptotic or homogenized models involving inhomogeneities of low contrast or vanishing size [2,38]. Moreover, as they provide a direct mathematical link between unknown inhomogeneities and remote measurements, they are also convenient for medium imaging inverse problems [5], for instance providing a foundation for contrast source inversion methods [32] or allowing rather explicit expressions of far-field patterns.In contrast with the vast existing literature on the mathematical aspects of boundary integral equations and their application to scattering by impenetrable obstacles characterized by Dirichlet, Neumann or impedant boundary conditions, comparatively few studies are available regarding the mathematical properties of volume integral equations. The well-posedness of volume integral formulations for various electromagnetic scattering problems is addressed in [33] f...