A WordPress theme controls the visual presentation and layout of a WordPress site. It consists of template files, stylesheets, functions, and optional assets (JavaScript, images, fonts). Themes define how content stored in the database is rendered in the browser.

A theme does not modify core WordPress functionality; instead, it uses WordPress APIs, hooks, and template hierarchy rules to display content.

Basic Theme Structure

A minimal theme requires:

  • style.css

  • index.php

Example: style.css (Theme Header)

/*
Theme Name: Example Theme
Theme URI: https://example.com
Author: Your Name
Author URI: https://example.com
Description: A minimal custom WordPress theme.
Version: 1.0
License: GNU General Public License v2 or later
Text Domain: example-theme
*/

The header comment identifies the theme in the WordPress admin panel.

Core Theme Files

Common theme files include:

  • index.php – Fallback template

  • functions.php – Theme functionality and hooks

  • style.css – Main stylesheet

  • header.php – Header template

  • footer.php – Footer template

  • sidebar.php – Sidebar template

  • single.php – Single post template

  • page.php – Static page template

  • archive.php – Archive template

  • 404.php – Not found template

Template Hierarchy

WordPress uses a template hierarchy to determine which file to load.

Example hierarchy for a single post:

  1. single-{posttype}.php

  2. single.php

  3. singular.php

  4. index.php

For a page:

  1. page-{slug}.php

  2. page-{id}.php

  3. page.php

  4. index.php

If a more specific template does not exist, WordPress falls back to a more general one.

The Loop

The Loop is used to retrieve and display posts.

Example: Basic Loop

<?php if ( have_posts() ) : ?>
    <?php while ( have_posts() ) : the_post(); ?>
        <h2><?php the_title(); ?></h2>
        <div>
            <?php the_content(); ?>
        </div>
    <?php endwhile; ?>
<?php else : ?>
    <p>No posts found.</p>
<?php endif; ?>

The Loop relies on the global $wp_query object.

functions.php

The functions.php file allows developers to extend theme functionality.

Enqueue Styles and Scripts

function example_theme_enqueue_assets() {
    wp_enqueue_style(
        'example-theme-style',
        get_stylesheet_uri(),
        array(),
        '1.0'
    );

    wp_enqueue_script(
        'example-theme-script',
        get_template_directory_uri() . '/js/main.js',
        array('jquery'),
        '1.0',
        true
    );
}
add_action('wp_enqueue_scripts', 'example_theme_enqueue_assets');

Using wp_enqueue_* functions ensures compatibility and avoids conflicts.

Theme Support Features

Themes should declare support for WordPress features.

function example_theme_setup() {
    add_theme_support('title-tag');
    add_theme_support('post-thumbnails');
    add_theme_support('custom-logo');
    add_theme_support('html5', array(
        'search-form',
        'comment-form',
        'comment-list',
        'gallery',
        'caption'
    ));

    register_nav_menus(array(
        'primary' => __('Primary Menu', 'example-theme')
    ));
}
add_action('after_setup_theme', 'example_theme_setup');