Scintillation properties of CsI:In single crystals have been investigated. Scintillation yield of CsI:In measured with the 24μs integration time is around 27,000ph/MeV, reaching the saturation at 0.005mol% of the activator. However, luminescence yield of CsI:In is close to CsI:Tl scintillation crystals, which is around 60,000ph/MeV. This difference is explained by the presence of an ultra-long afterglow in CsI:In scintillation pulse. Thermoluminescence studies revealed a stable trap around 240K that is supposed to be related to millisecond decay components. The best measured energy resolution of (8.5±0.3)% was achieved at 24μs peaking time for a CsI sample doped with 0.01mol% of In. Temperature stability of CsI:In radioluminescence intensity was found to be remarkably high. Its X-ray luminescence yield remains stable up to 600K, whereafter thermal quenching occurs. The latter property gives CsI:In a potential to be used in well logging applications.