WordPress upload_mimes filter hook example

functions.php

// Add this to the functions.php file of your WordPress theme
// It filters the mime types using the upload_mimes filter hook
// Add as many keys/values to the $mimes Array as needed

function my_custom_upload_mimes($mimes = array()) {

	// Add a key and value for the CSV file type
	$mimes['csv'] = "text/csv";

	return $mimes;
}

add_filter('upload_mimes', 'my_custom_upload_mimes');

Just leaving a note here for the Googlers: Since 'upload_mimes' is a filter, not a hook, it should be called via:

add_filter('upload_mimes', 'my_custom_upload_mimes');

Thank you @wunc, you are indeed correct =). We're the new owners and did not know about this page. We have modified it now.