functions.php in WordPress Themes

functions.php in WordPress Themes — a practical guide to WordPress functions.php with clear examples you can reuse in real projects.

WordPress Theme Development Series (9/96). Prefer one article? Read the complete WordPress theme development tutorial.

Short description

`functions.php` is the theme bootstrap file. Prefer small include files as the theme grows.

Theme setup sketch

<?php
add_action('after_setup_theme', function () {
    add_theme_support('title-tag');
    add_theme_support('post-thumbnails');
    register_nav_menus([
        'primary' => __('Primary Menu', 'acme-theme'),
    ]);
});