In an intrabody communication (IBC) system the human body is used as a part of a communication channel between the transmitters and receivers placed on the surface of the skin, in its vicinity, or implanted inside the user’s body. IBC systems use lower frequency band than standard wireless systems, and they have lower power consumption and lower range. Possible applications of IBC technology are broad: from biotelemetry and medicine to the communication between various electronic devices and security systems. This doctoral thesis is focused on analysis and modelling of a transmission path of an intrabody communication system, and on the design of very low power transmitters and receivers. Transmission characteristic of the capacitive IBC system depends on the tissue characteristics and signal path, defined by the positions of the transmitter and receiver, placement of the transmitter and receiver electrodes on the body, and surrounding environment. A procedure proposed for measuring IBC channel transmission characteristic in the frequency range from 100 kHz to 100 MHz provides galvanic decoupling of the measuring equipment from the IBC channel. Using a proposed measurement procedure, the influences of the type, size, and position of the transmitter and receiver electrodes, and the influence of the environment were investigated and theoretically explained. The conclusions were confirmed by the in vivo measurements in a realistic communication scenario, on a larger number of test subjects with different anatomical characteristics, for several static and dynamic body positions. Employing the measurement results analysis, a model of a capacitive intrabody communication system operating at discrete frequencies up to 100 MHz, based on lumped parameters and transmission lines was created. The guidelines for IBC transmitter and receiver design, optimal in the sense of power requirements, signal transmission quality, and dimensions were given, based on the developed model and in vivo measurements. Finally, the results of this thesis were applied in the development of an operating IBC system prototype.