The study of particle-level interactions in suspension flows enables a better understanding of complex collective phenomena that arise, such as spontaneous formation of non-uniform, anisotropic structure and particle size segregation. These phenomena have important implications for materials processing and the physiology of microcirculation in blood flow. In all cases, particle-particle and particle-wall hydrodynamic interactions play an important role in determining the type of flow-induced structure that is observed. Experiments and simulations have revealed a variety of microstructures that depend on intrinsic particle parameters and imposed flow characteristics. I will present a pairwise theory and show examples of flow-induced particle structures that are predicted. In the systems that I will discuss, particle size is usually small enough such that the governing equations of motion are linear and reversible. Under these conditions, pair interactions of spherical particles lead to symmetric trajectories with zero net cross-flow displacements and thus no structuring. However, short-range phenomena such as surface roughness, particle deformation, permeability, or colloidal forces can break the symmetry of particle trajectories, resulting in net cross-flow particle displacements. These displacements generate particles fluxes down particle-concentration and shear-rate gradients and a Boltzmann-type conservation equation governs the spatial evolution of the particles in suspension. Our simplified theory qualitatively explains certain flow-induced particle structuring in suspensions and its predictions are shown to be in qualitative agreement with experiments and numerical simulations.