This book explores the rich history of the keyword from its earliest manifestations (long before it appeared anywhere in Google Trends or library cataloging textbooks) in order to illustrate its implicit and explicit mediation of human cognition and communication processes. The author covers the concept of the keyword from its deictic origins in primate and proto-speech communities, through its development within oral traditions, to its initial appearances in numerous graphical forms and its workings over time within a variety of indexing traditions and technologies. The book follows the history all the way to its role in search engine optimization and social media strategies and its potential as an element in the slowly emerging semantic web, as well as in multiple voice search applications. The author synthesizes different perspectives on the significance of this often-invisible intermediary, both in and out of the library and information science context, helping readers to understand how it has come to be so embedded in our daily life.