Search Engine Optimization (or SEO) is the way you optimize your website to gain high rankings in search results. So if your business is about sunglasses, you would do on-site optimization (like modifying your page title, meta description, keyword density on each page) and off-site optimization (like link building with Sunglasses as your link text) to boost your website higher up the list when people search for sunglasses.Internet marketing is marketing your site on the internet. This can be done in a number of ways, including social media networks (Twitter, Facebook, etc.), creating Youtube videos that encourage visitors to come to your site, creating blog articles & submitting them to Digg hoping they go to the front page and ultimately lead to people coming to your site, getting a banner advertisement on a high traffic site that will get you visitor referrals, etc.They are both tied together very closely, as creating social networks and bookmarks to your site also builds links which helps with SEO. For example, you can create profiles on DoFollow social networks such as LinkedIn - this not only markets your site to your LinkedIn connection, but also creates a valuable backlink to your website which counts as a "vote" for your site in search engine result position, or SERP's (assuming that your LinkedIn profile is fully available to the public.You can learn more about link building with DoFollow social networks and more at the source site.