UV and EUV observations of stellar coronal structure and activity

Ultraviolet (HST, FUSE) and extreme-ultraviolet (EUVE) observations of stellar coronae and flare-related activity are reviewed. UV coronal forbidden lines, e.g. Fe XVIII 975 Å, Fe XIX 1118 Å, and Fe XXI 1354 Å, are commonly detected in active dwarfs and giants; these lines currently provide the only resolved spectroscopic diagnostics of conditions within stellar coronae. The UV coronal lines generally have widths consistent with thermal broadening and are unshifted. Only tantalising glimpses of flare-related motions have been detected. Stellar coronal temperature, density, and emission measure distributions are significantly different from quiescent solar coronal conditions. Stellar coronae are magnetically-confined plasmas with substantially higher heating rates and temperatures than encountered in the Quiet Sun. Conditions are similar to solar flares but the question of the flare contribution during "quiescence" is still unresolved. The statistical properties of stellar flaring and the relationship between events seen in different atmospheric regions are described.