Next generation of IACT arrays: scientific objectives versus energy domains

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.