Electronic communication is ubiquitous in homes, offices and urban environments. You probably regularly use mobile devices, Wi-Fi and broadband. What makes such forms of communication possible? How do they relate to each other? Why is their performance so variable? This module gives you an insight into these and other questions, by looking at the fundamental principles of communications technologies. Through these principles you will gain an insight into the possibilities and constraints of modern communications technology. This module complements other modules relating to networking, human-computer interaction, and pervasive computing.