  The Advanced X-ray Imaging Satellite (AXIS) is a Probe-class concept that
will build on the legacy of the Chandra X-ray Observatory by providing
low-background, arcsecond-resolution imaging in the 0.3-10 keV band across a
450 arcminute$^2$ field of view, with an order of magnitude improvement in
sensitivity. AXIS utilizes breakthroughs in the construction of lightweight
segmented X-ray optics using single-crystal silicon, and developments in the
fabrication of large-format, small-pixel, high readout rate CCD detectors with
good spectral resolution, allowing a robust and cost-effective design. Further,
AXIS will be responsive to target-of-opportunity alerts and, with onboard
transient detection, will be a powerful facility for studying the time-varying
X-ray universe, following on from the legacy of the Neil Gehrels (Swift) X-ray
observatory that revolutionized studies of the transient X-ray Universe. In
this paper, we present an overview of AXIS, highlighting the prime science
objectives driving the AXIS concept and how the observatory design will achieve
these objectives.
