Otto on WordPress has compiled a list of the absolute minimum requirements every WordPress theme should have:

Too often I see themes missing the absolute minimum requirements to make the theme actually work properly. So I figured I’d make a list of things that ALL WordPress themes need to have in them, every time. These are [...]

Here’s a neat discovery by Andrew Ozz: you can actually style the content of the WordPress WYSIWYG editor so that it displays how text and images will actually look like once posts are published. Matt Thomas, who leads the development for the new default WordPress “2010″, calls it WYSIWYRG (what you see is what you [...]

BloggingPro has a great rundown of the newest theme files introduced in the latest version of WordPress. Here’s the short list:

The category-slug.php template: Before, theme authors were limited to using category dependent theme files that used the category ID. In WP 2.9, category slugs can now be used in the category ID’s place. That’s a [...]

Two beta versions of WordPress 2.9 are out in the wild, so you know the final release will be announced soon. Have you looked at the newest features in WP 2.9 yet? If not, check out Technosailor’s round-up. The big news for WordPress theme authors is that post images are now integrated into the core. [...]

It’s official, WordPress themes are GPL too. Matt Mullenweg announced at the Development Blog that after consulting with the Software Freedom Law Center, it was determined that “PHP in WordPress themes must be GPL” although “artwork and CSS may be but are not required”. This means that WP theme code can be modified and distributed [...]

The latest version of WordPress, version 2.8 and codename “Baker”, is now out. If you haven’t updated yet, you might want to do so now. One of the biggest features in this version is the ability to install WordPress themes from within the admin dashboard, just like plugins.
Theme authors will also be happy to [...]

Spectacu.la and Justin Tadlock have reported that 200 free WordPress themes were removed from the official theme directory at WordPress.org, despite being complient with the GPL. As it turns out, there’s a more specific qualification to the list.
Thord Daniel Hedengren of The Blog Herald contacted Matt Mullenweg for clarification on the matter:

I emailed Matt Mullenweg, [...]

WordPress 2.7 “Coltrane” is finally out. And designers, you know what that means: time to update those themes! Old ones shouldn’t break with the new version of WordPress (if you’ve updated them for WP 2.6), but it’s an added incentive for bloggers to download WP 2.7-ready themes.
Read the WordPress Codex article on Migrating Plugins [...]

Navigation is one of the most important aspects of a WordPress theme, since users need to find their way around blogs. But before WordPress 2.7, there wasn’t really an automated way of doing this. You had to use the wp_list_pages() function and/or hardcode links into your theme files.
But that’s going to change with the [...]