  It is arguably in the X-ray regime that Narrow-line Seyfert 1 galaxies
(NLS1s) exhibit the most extreme behaviour. Spectral complexity, rapid and
large amplitude flux variations, and exceptional spectral variability are well
known characteristics. However, NLS1s are not eccentric, but form a continuous
sequence with typical Seyfert 1 galaxies. Understanding the extreme behaviour
displayed by NLS1s will provide insight to the general AGN phenomenon. In this
review, I will examine some of the important NLS1 X-ray discoveries over the
past twenty years. I will then explore recent work that looks at the nature of
the primary X-ray source (i.e. the corona) in NLS1s, demonstrating how the
corona can be compact, dynamic, and in some cases consistent with collimated
outflow. X-ray observations of NLS1s will be key in determining the nature of
the corona, resolving the disc-jet connection, and determining the origin of
the radio loud/quiet dichotomy in AGN.
