Supercapacitors, Li-ion batteries, gas sensors, and electrochromic devices are expected to play a major role in the development of sustainable technologies. Recent progress has demonstrated that nanostructured nickel oxides are very promising candidates for efficient energy conversion and storage systems. Recently, there is a growing interest in nickel oxide nanoparticles due to their unique physical and chemical properties. In this work, the synthesis of nickel oxide nanoparticles is primarily categorized with the preparation method. This review also provides a comparative overview of the influence of technological conditions on the properties of nickel oxide nanoparticles.