  Several key motivations and perspectives of ground based gamma-ray astronomy
are discussed in the context of the specifics of detection techniques and
scientific topics/objectives relevant to four major energy domains -- very-low
or \textit{multi-GeV} ($E \leq$ 30 GeV), low or \textit{sub-TeV} (30 GeV - 300
GeV), high or \textit{TeV} (300 GeV - 30 TeV), and very-high or
\textit{sub-PeV} ($E \geq$ 30 TeV) intervals -- to be covered by the next
generation of IACT arrays.
