Link Development is all about incoming links or as they are sometimes called; "Inbound Links" or "Back Links". These are the links on other sites that link back to your site.

Before Google's appearance, search engines used a search algorithm called Meta search. The search engines would crawl only the content (keywords) between Meta tags placed on sites. This led to search engine abuse (spamming) by inserting unrelated keywords into Meta tags. An example would be a search for "Used Cars" resulting in an Adult web site.

Search engines fought spammers by developing advanced crawling algorithms/systems. These new technologies would look between Meta tags and also at actual on-page content. Spammers then expanded their methods to make websites rank higher using techniques called Hidden Text, Hidden Links, White Text on White Background, to name a few.

Google engineers introduced another algorithm to their search engine model whereby instead of searching for keywords in Meta tags or on-page content, they also looked at the keywords within the anchor text (incoming link text) of incoming links. If the keywords searched matched the keywords in the anchor text of incoming links, then your site would show up.

Again, spammers figured out the algorithm and starting planting links on every other page of a site, even if the pages were not related to the site theme. In July of 2003, Google engineered a massive update in their search engine. It was called the Florida Update and many highly ranked websites suddenly lost their positions and instead appeared on the 100th - 200th Google page results. Google has become the most popular search engine due to its relevancy and accuracy of search results. This technology has also been implemented by other search engine giants, Yahoo and MSN.

The SEO industry now understands and believes that it is not only important to have as many incoming links as possible, but the links must come only from theme related sites. In order to make a site rank high on search engines, link development is a must. It is considered the most complicated and slowest process of search engine optimization but very successful in the long run.

An apt analogy would be links for votes. The more links/votes a site/candidate possesses, the more successful their campaign will be.