  Hard X-ray and low-energy gamma-ray coded-aperture imaging instruments have
been highly successful as high-energy surveyors and transient-source
discoverers and trackers over the past decades. Albeit having relatively low
sensitivity as compared to focussing instruments, coded-aperture telescopes
still represent a very good choice for simultaneous, high cadence spectral
measurements of individual point sources in large source fields. Here I present
a review of the fundamentals of coded-aperture imaging instruments in
high-energy astrophysics. Emphasis is on fundamental aspects of the technique,
coded-mask instrument characteristics, and properties of the reconstructed
images.
