By default, Drupal comes with 5 content "regions": header, footer, left sidebar, right sidebar, and content. In many cases it is convenient to have several additional regions for more granular control over content location.

Sometimes we need to have certain blocks to always appear above or below the content, so let's add a few new regions!

For Drupal 5.x:

Open the template.php file in your theme's folder and add the following function:

function themeName_regions()
{
    return array(
        'left' => 'Left sidebar',
        'right' => 'Right sidebar',
        'content' => 'Content',
        'header' => 'Header',
        'footer' => 'Footer',
        'top_content' => 'Top Content',
        'bottom_content' => 'Bottom Content'
    );
}

Now just replace 'themeName' with your theme's name, and you're good to go!

For Drupal 6.x:

Drupal 6 comes with a new theme registry, so the process is slightly different from the one for Drupal 5.x. Open the .info file in your theme's folder, and add the following:

regions[left] = Left sidebar
regions[right] = Right sidebar
regions[content] = Content
regions[header] = Header
regions[footer] = Footer
regions[top_content] = Top Content
regions[bottom_content] = Bottom Content

Whenever you create new theme functions or templates in Drupal 6 you must clear the registry by one of the following two methods:

• The clear button located at "Administer -> Site configuration -> Performance"
• Calling drupal_rebuild_theme_registry(). (hint: place this at the top of your template.php file while you're developing the site & remove from production)

Update: At this point the regions are available, but are not being output anywhere, so let's open up page.tpl.php and add the following:

print $top_content;
print $bottom_content;

(Thanks for the reminder, eL!)