The emerging in vivo communication and networking system is a prospective component in advancing healthcare delivery and empowering the development of new applications and services. In vivo communications is based on networked cyber-physical systems of embedded devices to allow rapid, correct and costeffective responses under various conditions. This chapter presents the existing research which investigates the state of art of the in vivo communication. It focuses on characterizing and modeling the in vivo wireless channel and contrasting it with the other familiar channels. MIMO in vivo is also of cencern in this chapter since it significantly enhances the performance gain and data rates. Furthermore, this chapter addresses in vivo nano-communication which is presented for medical applications to provide fast and accurate disease diagnosis and treatment. Such communication paradigm is capable of operating inside the human body in real time and will be of great benefit for medical monitoring and medical implant communications. Consequently, propagation at the Terahertz (THz) frequency must be well understood as it is considered the most promising band for electromagnetic nano-communication models.