Modern view of the warm ionized medium

We review the observational evidence that the warm ionized medium (WIM) is a major and physically distinct component of the Galactic interstellar medium. Although up to ~20% of the faint, high-latitude H-alpha emission in the Milky Way may be scattered light emitted in midplane H II regions, recent scattered light models do not effectively challenge the well-established properties of the WIM.
Comment: To appear in the proceedings of IAU Special Session 12: Modern Views of the Interstellar Medium. Two pages, no figures