Supplementary to matter and energy, information is the third essence for modeling the natural world. An emerging discipline known as cognitive informatics (CI) is developed recently that forms a profound interdisciplinary study of cognitive and information sciences, and tackles the common root problems sharing by informatics, computing, software engineering, artificial intelligence, cognitive science, neuropsychology, philosophy, linguistics, and life science. CI focuses on internal information processing mechanisms and the natural intelligence of the brain. This paper describes the historical development of informatics from the classical information theory and contemporary informatics, to CI. The domain of CI, and its interdisciplinary nature are explored. Foundations of CI, particularly the brain versus the mind, the acquired life functions versus the inherited ones, and generic relationships between information, matter, and energy are investigated. The potential engineering applications of CI and perspectives on future research are discussed. It is expected that the investigation into CI will result in fundamental findings towards the development of next generation IT and software technologies, and new architectures of computing systems.