JQuery Not Working in Wordpress

Have you added the actual jQuery script file?

There are a number of ways to do this, but I usually use the following method by including this code in the functions.php file.

<?php
    function add_jquery() {
       wp_enqueue_script( 'jquery' );
    }    

    add_action('init', 'add_jquery');
?>

Here is also a good resource for more jQuery + Wordpress usage:

Make sure WP itself (or another installed plugin) does not have an already embedded jQuery version that conflicts with yours.. View the source of your page and make sure only one jQuery version is loaded. Should go w/o problems.

By using wp_enqueue_script you are sure the jQuery library is loaded ONCE. You can see here how to load a JS file.

Beside the way mentioned by Paul Sham which is absolutely correct, following way is also helpful which is also describe at THIS link.

function include_jQuery() {
    if (!is_admin()) {
        // comment out the next two lines to load the local copy of jQuery
        wp_deregister_script('jquery'); 
        wp_register_script('jquery', ' false, '1.8.3'); 
        wp_enqueue_script('jquery');
    }
}
add_action('init', 'include_jQuery');

if( !is_admin()){
  wp_deregister_script('jquery');
  wp_register_script('jquery',       (""), false, '1.3.1');
  wp_enqueue_script('jquery'); 
}

put this code in your current wordpress theame's function.php file in between

I find the other one, write this at the beginning of your script. $ = jQuery.noConflict();