Once keyword research has been conducted and the website has been optimized, the ongoing component of an SEO program is link building. Link building is necessary because inbound links pointing to a website are what convey trust to the search engine spiders. The search spiders crawl the web link to link and the more quality links that are out there, the more time the search spiders will end up back on your site. Inbound links are also what help generate traffic to your site.