This document provides an introduction to communication theory. It defines communication as the process of sending and receiving messages, with shared understanding being key. Verbal communication uses words, while nonverbal communication relies on body language and cues. Group communication occurs between two or more people, with intimacy depending on group size. Mass communication extends group communication through tools like newspapers, TV, radio, films and the internet. The document also defines theories as abstract understandings of the communication process that explain what is known and how it is known. Commonsense, working and scholarly theories are described. Finally, the document notes some limitations of communication and provides tips for dealing with communication barriers.