  The high energy X-ray and ultraviolet (UV) radiation fields of exoplanet host
stars play a crucial role in controlling the atmospheric conditions and the
potential habitability of exoplanets. Major surveys of the X-ray/UV emissions
from late-type (K and M spectral type) exoplanet hosts have been conducted by
the MUSCLES and Mega-MUSCLES Hubble Space Telescope (HST) Treasury programs.
These samples primarily consist of relatively old, ``inactive'', low mass
stars. In this paper we present results from X-ray observations of the coronal
emission from these stars obtained using the Chandra X-ray Observatory, the
XMM-Newton Observatory, and the Neil Gehrels Swift Observatory. The stars
effectively sample the coronal activity of low-mass stars at a wide range of
masses and ages. The vast majority (21 of 23) of the stars are detected and
their X-ray luminosities measured. Short-term flaring variability is detected
for most of the fully-convective (M $\leq$ 0.35 M$_{\odot}$) stars but not for
the more massive M dwarfs during these observations. Despite this difference,
the mean X-ray luminosities for these two sets of M dwarfs are similar with
more massive (0.35 M$_{\odot}$ $\leq$ M $\leq$ 0.6 M$_{\odot}$) M dwarfs at
$\sim$5 $\times$ 10$^{26}$ erg s$^{-1}$ compared to $\sim$2 $\times$ 10$^{26}$
erg s$^{-1}$ for fully-convective stars older than 1 Gyr. Younger,
fully-convective M dwarfs have X-ray luminosities between 3 and 6 $\times$
10$^{27}$ erg s$^{-1}$.The coronal X-ray spectra have been characterized and
provide important information that is vital for the modeling of the stellar EUV
spectra.
