Today, over 25 million books in the public domain are available online via Google Books. The Google Books Ngram Viewer is a tool that allows researchers, along with the generally curious, to perform a text search on all of these books in order to uncover major trends, vocabulary, and themes over time. By simply typing a name or word into the search box (e.g. "Shakespeare") and selecting a time frame (e.g. the years 1700-1900) users can instantly view a line graph to see how often that word appeared in books by publication date. Users can also select a narrow date range (which will appear underneath the graph) in order to explore specific titles featuring the selected term. Google Books Ngram Viewer allows users to compare the frequency of multiple keywords or names by using commas to separate variables.