Page Rank is a link analysis algorithm that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of "measuring" its relative importance within the set. The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is also called the Page Rank of E and denoted by PR(E).

Page Rank was developed at Stanford University by Larry Page (hence the name Page-Rank) and later Sergey Brin as part of a research project about a new kind of search engine. The project started in 1995 and led to a functional prototype, named Google, in 1998. Shortly after, Page and Brin founded Google Inc., the company behind the Google search engine. While just one of many factors which determine the ranking of Google search results, Page Rank continues to provide the basis for all of Google's web search tools.

Page Rank is only a score that represents the importance of a page, as Google estimates it (By the way, that estimate of importance is considered to be Google's opinion and protected in the US by the First Amendment. When Google was once sued over altering Page Rank scores for some sites, a US court ruled: "Page Ranks are opinions--opinions of the significance of particular Web sites as they correspond to a search query....the court concludes Google's Page Ranks are entitled to full constitutional protection.

Page Rank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves important. weigh more heavily and help to make other pages important. In other words, a Page Rank results from a ballot among all the other pages on the World Wide Web about how important a page is. A hyperlink to a page counts as a vote of support. The Page Rank of a page is defined recursively and depends on the number and Page Rank metric of all pages that link to it ("incoming links"). A page that is linked to by many pages with high Page Rank receives a high rank itself. If there are no links to a web page there is no support for that page. Google assigns a numeric weighting from 0-10 for each webpage on the Internet; this Page Rank denotes a site.and its importance in the eyes of Google. The scale for Page Rank is logarithmic like the Richter Scale and roughly based upon quantity of inbound links as well as importance of the page providing the link. Numerous academic papers concerning Page Rank have been published since Page and Brin has original paper. In practice, the Page Rank concept has proven to be vulnerable to manipulation, and extensive research has been devoted to identifying falsely inflated Page Rank and ways to ignore links from documents with falsely inflated Page Rank.

Alternatives to the Page Rank algorithm include the HITS algorithm proposed by Jon Kleinberg, the IBM CLEVER project and the Trust Rank algorithm.

It considers links to be like votes. In addition, it considers that some votes are more important than others. Page Rank is Google's system of counting link votes and determining which pages are most important based on them. These scores are then used along with many other things to determine if a page will rank well in a search. Don't like me speaking for Google? No worries. When Google talks about Page Rank at its site, it often links to the Google Technology page, which says: The heart of our software is Page Ran, a system for ranking web pages developed by our founders Larry Page and Sergey Brin at Stanford University. And while we have dozens of engineers working to improve every aspect of Google on a daily basis, Page Rank continues to play a central role in many of our web search tools.

Page Rank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page's value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at considerably more than the sheer volume of votes, or links a page receives; for example, it also analyzes the page that casts the vote. Votes cast by pages that are themselves "important" weigh more heavily and help to make other pages "important." Using these and other factors, Google provides its views on pages' relative importance. I've covered the two main ways that Page Rank is visible to searchers plus mentioned that behind the scenes, it is one of many factors that helps rank web pages. How pages are ranked is, of course, of keen interest to SEOs. Sadly -- so, so sadly -- far too many SEOs fixated on the Page Rank meter when it came out first through the Google Directory and then later in December 2000 via the Google Toolbar. They focused on getting links from high PR pages without realizing that Page Rank alone wasn't enough. The issue of links and search engines, in particular the perception of Google's use of links, has gotten out of hand. For many, the original reason of linking has been lost out of the desire to simply do whatever they believe Google might like.

All major crawler-based search engines leverage links from across of the web, but none of them report a static "importance" score in the way Google does via its Google Toolbar. That score, while a great resource for surfers, has also provided one of the few windows into how Google ranks web pages. Some webmasters, desperate to get inside Google, keep flying into that window like confused birds, smacking their heads and losing their orientation.... Site owners are using the toolbar to find "good" sites that they should get links from, regardless of the fact that link context is also important, not to mention many, many other factors that are used by Google to rank a web page. Other site owners, getting a gray PR0 toolbar for their site, immediate assume the worst, that they've been blacklisted.

Enough please, enough. Forget the Google Toolbar meter. Forget about worrying over "good" links and "bad" links according to Google. Just forget Google, when it comes to link building.