The effect of spin injection into d-wave, p-wave, and s-wave superconductors is studied here. A theory is developed which treats the interplay between the bulk and boundary spin transport, as well as the interplay between pair and single-particle transport at the boundary. This theory is used to study the relationship between Andreev reflection and the linear-response spin-injection characteristics. Among the quantities of interest are, the amount of injected magnetization (m), the induced spin-dependent current (I s), and the induced boundary voltage (Vs). In general, Andreev reflection makes each of these three quantities depend on a different combination of the boundary and bulk contributions. The conditions are identified under which some of these quantities that depend solely on the bulk properties can be isolated. A correlation between the Andreev bound states and the spin-injection characteristics is established, which implies a strong directional dependence of spin injection into high-temperature superconductors and in p-wave superconductors.