Healthcare is one of the industries that has embraced and benefitted the most from improved internet connectivity and usage. Since the number of healthcare service seekers across the world is growing at a rapid pace, service providers rely on the internet-connected ecosystem, which is also known as the critical health infrastructure, Internet of Health Things (IoHT) or Internet of Medical Things (IoMT). The importance of IoHT was highlighted during the COVID-19 pandemic. While these technologies provide huge benefits, it goes hand in hand with malicious xploitation. Cybercrime costs are projected to hit 1 trillion USD per month by 2031. Healthcare is one of the most susceptible industries for cybercrime. There has been a massive surge in cyber-attacks, and newer variants of cyber threats are emerging. This book addresses the challenges associated with modern healthcare, which will provide a bigger picture of the evolution, trends, techniques, impact on critical infrastructures, national security, countermeasures, and open research directions in this area. In addition, it serves as a single source of reference of knowledge on the topic.