The COVID-19 pandemic is not only a threat to our health and economy, but also has strong implications for defence and security. Indeed, defence leaders have highlighted a second fight surrounding the spread of COVID-19, namely disinformation and preparing to face adversaries willing to exploit the public health crisis for nefarious purposes. The current pandemic is a breeding ground for the propagation of disinformation, as it represents the first major global health event in which large social media platforms have become the main distributor of information. This multi-national edited volume consists of contributions from Defence Science, academia and industry, including NATO Headquarters, United States, Netherlands, Singapore, United Kingdom and Norway. The content is aimed at a diverse audience, including NATO members, researchers from defence and security organizations, academics, and militaries including analysts and practitioners, as well as policy makers. This volume focuses on various aspects of COVID-19 disinformation, including identifying global dominant disinformation narratives and the methods used to spread disinformation, examining COVID-19 disinformation within the broader context of the cognitive domain, examining the psychological effects of COVID-19 disinformation and COVID-19 disinformation on instant messaging platforms, along with examining various countermeasures to disinformation.