Link-building is an important method in Search Engine Optimization. Essentially, it means that in order to make your site stand out from the crowd, you must have links from trusted, well-established sites. This is often an involved process since there are no hard and fast rules in SEO and search engines change algorithms all the time, but by providing quality content and attracting quality links, link-building will work for you.

Backlinks are inbound links received by one site’s web page from another site’s web page. Backlinks show you which other web pages have links to your own pages and the number as well as quality of backlinks that a page has often helps to determine its placement on the SERP (search engine results page).

Link popularity is simply the assessment of the number and quality of websites that link to a specific site. This is one of the factors used in determining the importance/value of a site (or page) and its corresponding position on the search engine results page. The more links and the higher their quality, the better the link popularity.

Google PageRank (PR) is one of the techniques that Google uses to evaluate the importance of a web page. Pages are assigned a numerical value (from 0 to 10), a PageRank, which corresponds to how important Google determines a page to be. Thus, a higher PR indicates a higher importance which then increases the likelihood of a page’s ranking among the top search results. Note that Google’s algorithm is vastly more complicated than this, and that the stated Google PageRank as seen on the Google Toolbar should be used only as a rough estimate and reference.

Building relevant, high quality links is one of the foremost considerations of SEO and there are numerous methods that are effective in getting other websites to link to yours. Here are some useful link-building tips that can help you attract the links you want:

• Submit your site to a variety of relevant web directories, including niche-specific ones.
• Write informative press releases and submit them to PR sites.
• Swap links with related sites.
• Submit pertinent articles; make yourself known as an authority.
• Create social media profiles.
• Utilize the social bookmarking system.
• Create compelling a theme or widget and make it available for free.
• Post comments on blogs with a subject matter relevant to your own.
• Partner with related blogs and guest post.
• Sponsor contests.

Commenting on forums and blogs can help drive direct traffic to your site, but this is a strategy that will work best only if your comments are relevant to the topic and actually add value. You can attract quality links by focusing on your particular niche’s forums and blogs, building relationships with fellow bloggers and posting your own great content on your blog that other bloggers can link to and comment on. In short, the more you become a voice in forums related to your industry, the better links and visibility your site will enjoy.

Link building can be an arduous task, however sometimes the best way to get other sites to link to yours is simply to go out and ask a bunch of websites to link to you. Webmasters get pestered by endless requests for link exchanges, however, so when you contact the webmasters of the sites you’re interested in be professional and legitimate and polite in your requests.

Buying backlinks has become one of the most popular methods for link-building. While Google acknowledges that "buying and selling links is a normal part of the economy of the web," they also stress that only "when done for advertising purposes, and not for manipulation of search results" will that not violate Google’s webmaster guidelines. So if you’re considering buying backlinks for the latter purpose, is it imperative to find the most reputable services out there.

There are many backlink checker tools on the internet, among the most useful of which are Google’s toolbar and Yahoo! Site Explorer.

As the name implies, one-way links are links to your site from other sites, which do not receive a link to your site in return. These are coveted links since the message that one-way linking conveys – especially when the website that’s linking is a well-established one – is that other sites have found yours to be important or interesting and this increases your link popularity considerably.

Reciprocal links, also known as link exchanges, link swaps and link partners, are the exchanged links of two websites. They help direct traffic to the site, however only marginally increase your site’s search engine rankings.