The Google Books service is a massive online database of digitized books and magazines. These books have been scanned as part of a collaboration between Google and many high-profile university and public libraries. Books can also be submitted to the database by publishers and authors.
Things to note about Google Books:
Unlike most other book catalogs, Google Books allows for full-text searching across the entire database.
Books out of copyright are usually available for viewing and/or download.
Copyrighted books allow for a limited preview. This can still be useful for reading chapters or table of contents.
Advanced Search
As Google Books provides full-text searching it has a much higher recall than other catalogs. The amount of results retrieved can be overwhelming so use the advanced search feature to help search with more precision.
To find the advanced search function:
Conduct a basic search.
Click on 'Settings' underneath the search box and then select 'Advanced Search' from the drop down menu.
Google Books Ngram Viewer
The Google Books Ngram Viewer allows you to chart the frequencies of words and phrases used in books over time. The millions of digitized books in the Google Books project provide an enormous corpus of data to track these trajectories.
To use the Ngram Viewer:
Enter your search terms (with a comma between each one).
Select a date range (most recent date allowed is 2008)
Select whether you wish your search terms to be case-sensitive or not
The chart below shows the frequency of the terms 'science', 'religion' and 'politics' (case-insensitive) between 1800 and 2008.
Google Ngram Viewer also allows advanced searching using special search tags. For example:
Use * to act as a wildcard. The Ngram Viewer will return the 10 most popular substitutions for this wildcard.
You can also distinguish between parts of speech by using special tags to search for nouns (_NOUN_), verbs (_VERB_), adjectives (_ADJ_) and more.
These search tags can often be combined for more powerful searching. For instance, if you wanted to see who was the most referenced President of the twentieth century (in the English language corpus) you could perform the following search:
There are many more advanced search tags to explore in the Ngram Viewer. For a full list and how to use them, check out Google's instruction page for the Ngram Viewer.
Read more about Google Books Ngram Viewer and how you can use this powerful tool in this article from The Atlantic.
Note: Despite digitizing several million books, the Google Books project is only a selective sampling of all the books written in history. For more information about potential pitfalls and limitations of using Google's Ngram Viewer for research, check out this Wired article.