Unlike other mediated communication technologies which have been analyzed over decades or centuries rather than years, IM communication has been the focus of relatively few academic inquiries, and very little is known about the content of "real world" instant messages. This study used quantitative content analysis software to create a linguistic profile of college student instant messaging (IM) behaviors to investigate sex differences in text-based communication. Conversations of 100 participants were logged over a period of 14 days. Linguistic indicators of psychological states, differences in affective language use by conversation dyad type, and gender differences within the context of IM were investigated. A multidimensional profile of linguistic characteristics of IM conversation was developed, and a comparison was made between the linguistic characteristics of IM, emotion writing, control writing, and talking. This book is addressed to professionals involved with mediated communication and the development of systems that enable mediated communication. It is also directed towards researchers in communication, gender, linguistics, and interaction technology.