Exchanging links between Web sites used to be a common and useful tactic for improving search engine ranking, but not any more.

A link exchange is an online promotional tactic in which a webmaster posts a link on his or her site to another site. In exchange, the other site posts a link in a similar location back to the first site.

The practice had two major benefits. One is that the search engines would see the link as a "vote" in favor of the receiving site. The other is that visitors to one site may click on the link and go to the other site.

Google policies say that certain types of exchanges will in fact hurt a site's ranking:

• "Links intended to manipulate PageRank
• "Links to web spammers or bad neighborhoods on the web
• "Excessive reciprocal links or excessive link exchanging ("Link to me and I'll link to you.")
• "Buying or selling links that pass PageRank" (a Google measure of the importance of a page)

Instead, Google encourages sites to build quality content with the hope that other sites will voluntarily link to that content as part of a natural link-building process. As a result, "link baiting," a method of encouraging natural link building, has become more popular rather than link exchanges.

But link exchanges still take place and do provide some remaining benefit with traffic from visitors that click on the links. The more prominent and relevant the link, the more likely a site visitor will click on it.

Links should use 'rel="nofollow"' in the anchor tag to prevent passing PageRank from one site to the other. Google will recognize the link and credit it as a legitimate backlink. One way of confirming this is by looking at the backlink list in a site's Google Webmaster Central account.