Telecommunication is the emission, transmission at a distance and reception of information, in any given space, where the information is conveyed by means of a material transmission medium for a wired transmission, or non-material for a wireless transmission. The transmission media affect the transmitted signals by different types of perturbations and degradations due mainly to their characteristics. In order to minimize the effect of the transmission medium on the transmitted information, communication systems are set up. The signals exchanged via a communication system were initially of analog nature (analog communication). A technique appeared to facilitate the restitution of the received signal with a quality close to that of the emitted signal is the digitization of the analogical signal (digital communication). This book aims at giving a global vision of the principles of telecommunications.