How To Create A Custom Taxonomy In WordPress — Smashing ... How To Create A Custom Taxonomy In WordPress — Smashing Jan 4, 2012 - In WordPress, you can create (or “register”) a new taxonomy by using the register_taxonomy() function. Each taxonomy option is documented in detail in the WordPress Codex. After adding this to your theme's functions.php file, you should see a new taxonomy under the “Posts” menu in the admin sidebar.