CMEs are multi-thermal with their primary features appearing in either hot or cool lines. Top panel: A hot CME is bright in the 335 Å (Fe xvi; ~3 MK), 94 Å (Fe xviii; ~6 MK), and 131 Å (Fe xxi; >10 MK) channels, but nearly invisible in the cooler lines (Reeves & Golub, 2011). Bottom panel: A cool CME is seen clearly in the 304 Å (He ii; ~50,000 K) channel and in 171 Å (Fe ix; ~0.6 MK), but only in absorption in Fe xii–xvi (~1–3 MK). In the 131 Å channel, the CME is visible due to emission from Fe viii (Su et al., 2015). Observations must detect plasma over this wide range of temperatures and be able to separate the components spatially.