Find the category name

Hopefully, really easy. Already have the category ID in a variable:

<?php global $wp_query;
$cat_ID = get_query_var('cat');
//echo $cat_ID;
?>

Just want to throw that variable into something like:
<?php get_cat_name($cat_ID) ?>

and get it to work.

For some reason, can’t get it to work, and can not find a solution in the codex.

Suggestions?

Thanks

Nadine