How to integrate WordPress template with CodeIgniter?

First step is to move CodeIgniter and the WordPress files in their own directory.

After that, put the following line at the top of your CodeIgniter’s index.php file. Change the path to wp-blog-header.php as needed to point to your wordpress’s root directory.

<?php
require('../wp-blog-header.php');

Then, you can use the following functions inside your views:

<?
get_header();
get_sidebar();
get_footer();    
?>

Other helper functions can also be found in WordPress’s documentation which can assist you in integrating the design.