HTML offers many of the conventional publishing idioms for rich text and structured documents, but what separate it from most other markup languages are its features for hypertext and interactive documents. This section introduces the link, the basic hypertext construct. A link is a connection from one Web resource to another. Although a simple concept, the link has been one of the primary forces driving the success of the Web. The web as they call it is a mesh of links. The wired world is now being counted for what it is. A Network. The more your pages are wired or integrated into the overall web linking architecture, the better it is from search engine ranking point of view. Google specially thrives on crawling on links. Its page rank is a measure of this.
When setting up the linking architecture of your site keep in mind that links are of two kinds:
1. Internal links
2. External links

Internal links: Internal links are links to other pages on the same web site. They are the bridges by which one page of your site connects to the other & more importantly outlines, which page of your site will connect to which other pages.

External links: External links are those that take you to another site. External links on the other hand are the community tools by which the online community votes for you by linking to you. The more popular you get is a function of more incoming links into your website. This in turn is interpreted by search engines as a measure of your online value creation.

Linking Attribute: It is always preferable to have a text link rather then a Graphic/Image link, because in a text link you can use Keywords as the text on which hyperlink is given. In effect you can make your anchor tag keyword rich. Anchor tags' text is a very important criterion in search engine ranking matrix.
Search engines look at not only how many people are linking to you, how important they themselves are but also what they are saying while linking to you. In fact search engines like Google have gone a step ahead. They not only look at the anchor tag but also the text surrounding it. Essentially they are trying to establish the relevance of that link to your pages content.
Another important aspect of the internal linking of your site is the sitemap. A sitemap is a page that contains links to every page on the site. There should be a link to the sitemap on every page, or at least on the homepage. A sitemap helps you to have an overview of your site linking architecture as well as it helps SE crawl the entire web site.

Internal linking architecture
There are three forms that can be assumed while planning the sites internal linking pattern.

Hierarchal: In this kind of Internal linking all the pages of the website are connected to the home page and home page is individually connected to all the pages of the website, but there is no linking between the pages of the website.

Looping: In this kind of Internal linking the home page is connected to the primary page and the primary page is connected to the secondary page and this process goes on till the last page and the last page is connected to the home page in this way a loop is formed.

Extensive inter linking: In this kind of Internal linking each page is connected to each other in the website. What kind of internal linking is preferable in a certain case is dependent on the objectives you are trying to achieve in terms of Page rank optimization, user navigation ease & site theme.One tip to bear in mind is that internal linking should reinforce the theme. One should not crosslink between the pages on the site which are unrelated by themes. This will dilute the theme intensity & affect the page rankings on SERPs.

Redundant Internal links: Two categories of internal links that should be guarded against are: broken links & dead links.

Broken links: Broken links are the links that are in the website and when they are clicked they don't open a webpage rather they show some error.

Dead links: Dead links are the links that are in the website and when they are clicked they don't open a webpage and they don't even show some error.

External linking: External linking on the other hand is more difficult to control & hence more valued by search engines. This is what really builds up the PR of the webpage. Good quality incoming links are craved by the online promotion experts all over.