Abstract: Efficient shadowing algorithms have been sought for decades, but most shadow research focuses on quickly identifying shadows on surfaces. This paper introduces a novel algorithm to efficiently sample light visibility at points inside a volume. These voxelized shadow volumes (VSVs) extend shadow maps to allow efficient, simultaneous queries of visibility along view rays, or can alternately be seen as a discretized shadow volume. We voxelize the scene intoa binary, epipolar-space grid where we apply a fast parallel scan to identify shadowed voxels. Using a view-dependent grid, our GPU implementation looks up 128 visibility samples along any eye ray with a single texture fetch. We demonstrate our algorithm in the context of interactive shadows in homogeneous, single-scattering participating media.