All documents available through Google Patents covers originate from the United States Patent and Trademark Office (USPTO), the European Patent Office (EPO), and the World Intellectual Property Organization (WIPO).
Google Patents covers the entire collection of granted patents and published patent applications from the USPTO, EPO, and WIPO. US patent documents date back to 1790, EPO and WIPO to 1978.
With Prior Art Finder, you can find documents related to a particular patent application or grant. The Prior Art Finder identifies key phrases from EPO, WIPO, and post-1976 US patent documents, combines them into a search query, and displays the results from Google Patents, Google Scholar, Google Books, and the rest of the web. And as another way to explore those collections, the Finder's "People" tab lets you search by inventor.