Microformats are a way of defining new data formats using existing standards and languages (ie. HTML and XML). It's a very exciting area of web development. The concept is relatively new, so there are really only a few formats out there (currently nine formats plus ten draft formats). There's also a lot of room for new formats to be created and used.

The idea is to use simple, easy, and predictable ways of defining new standards, rather than defining some complex impossible new standard. This way, the standard is something people can start using and benefitting from very easily and quickly. There's no need to go and change existing structures. Rather, microformats tend to be subtle adjustments to the way people tend to do things anyway.

The ultimate source of everything microformat-related is currently the the Microformats Wiki, and if it's your first time looking at microformats, I suggest you read the microformats entry. Since it's a Wiki, anybody can add new microformats, or contribute to existing ones.

I can't mention microformats without mentioning Tantek Çelik. He can be credited with the concept, and he still plays a very active role in defining and promoting new standards. He's the editor on the Wiki, and from what I can tell, he's co-created most if not all of the current microformats.

You may be familiar with the rel-nofollow standard. Google came up with the idea of adding rel="nofollow" to links in blog comments. This tells the Googlebot to ignore these links when calculating PageRank. This is intented to prevent comment spam, because spammers won't gain a higher PageRank by sticking their URL in comments.

The idea is perfectly simple. It uses an attribute built into HTML, the rel attribute, in a way that is consistent with its intended purpose. The HTML 4.01 spec says:

They give a list of link types, but afterwards they state:

As a result, the rel-attribute is a common method of implementing link-related microformats. Another example of a rel-attribute microformat is the Technorati rel-tag format. Technorati scans blog posts looking for links with rel="tag". The word or phrase within that link is used as a tag to describe the post. This blog uses such tags, and you can see them at the end of this post.

In the future, I'd like to discuss some more of these microformats and show more examples. Until then, I suggest you check out the Microformats Wiki and see if there's any microformats you can start using today.