Air-gapped networks are isolated, separated both logically and physically from public networks. For example, military, industrial, and financial networks. Although the feasibility of invading such systems has been demonstrated in past cyberattacks as covered by the media, communication of data to/from air-gapped networks is a challenging task to attackers to perpetrate. In this talk, we discuss various covert-channels for communication with air gapped networks, some advanced and difficult to mitigate. We will review the state-of-the-art research over electromagnetic, electric, magnetic acoustic, optic and thermal channels, and discuss each one’s countermeasures and feasibility. We also examine their characteristics and limitations, and analyze the relevance of these threats today and the likelihood of related cyber-attacks in the modern IT environment. We discuss the defensive countermeasures used to encounter such threats and close the article with an outlook on the subject in the context of the modern cyber-security arena.