Million degree plasmas are ubiquitous in the Universe, and examples include the atmospheres of white dwarfs (WDs); accretion phenomena in young stars (classical T-Tauri), cataclysmic variables (CVs) and active galactic nuclei (AGN); the coronae of stars; and the interstellar medium (ISM) of our own galaxy and of others. Understanding their nature is fundamental to astrophysics. This White Paper addresses primarily two Astro2010 Thematic Science Areas, SSE and GAN, and has ...