Recently, the concept of a nanonetwork has attracted large attention of researchers as it potentially offers low-cost solutions for a wide spectrum of current applications and enables numerous emerging ones. At present, however, all the sensor networks consist of a relatively small number of macroscale devices with their positions carefully pre-determined. The typical nanonetwork, on the contrary, can be envisioned as a swarm of nanomachines that are distributed in a random manner, which also can reach covered places, accomplish sensing directly inside a phenomenon or equip an application with enhanced control capabilities. To operate and monitor within a macroscale application area, information sharing between nanonetwork entities is required (likewise data transfer among human cells). Electromagnetic waves at microwave frequencies can potentially enable wireless communication between nanomachines even in vicious and hazardous environments. However, the paradigms of traditional microwave communication must undergo a substantial revision before being applied to nanotechnology: due to space restrictions, nanomachines have very strong power limitations and should be capable to operate on an extremely tight energy budget. This places a very strong restriction on the communication link power budget. Moreover, networking-level techniques capable of describing a connectivity and signal propagation in the 'topology-less' nanonetwork are currently missing. These two open issues served as primary motivating factors for this doctoral dissertation, which broadly focuses on the feasibility and development of electromagnetic-based communications for nanonetworks.