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 WordPress theme-specific things. I’m not including obvious stuff like HTML and such.

The list covers everything until the not-yet-released version 3.0, which lets you call the default comment form using comment_form() and support the built-in navigation menu.

Oldies include the likes of wp_head() and wp_footer(), and class functions like body_class() and post_class() have been around for several versions now—there’s no excuse not to include these. Meanwhile, trickier features lie in the comments.php template, but once you get the hang of it, you’ll get along fine.

Keep these in mind along with our own FWPT checklist!