Try as I might I cannot get my head around what the IteratorIterator class actually does. I understand that classes can implement Traversable so the engine knows it can loop using foreach and I realise that IteratorIterator is supposed to convert anything that is Traversable into an Iterator but I cannot for the life of me understand how. Take for example, the PDOStatement class; how would the standard Iterator methods (next, key, rewind, etc) be implemented to allow iteration over a PDOStatement? Sorry if my question is unclear, I am just struggling to grasp the exact reason for this class and the documentation on it is scant. Thanks, Will Update: Going through the phpt files, I found one test which uses IteratorIterator: <?php $root = simplexml_load_string('<?xml version="1.0"?> <root> <child>Hello</child> <child>World</child> </root> '); foreach (new IteratorIterator($root->child) as $child) { echo $child."\n"; } ?> The expected output is: Hello World I don't really follow how the IteratorIterator construct takes $root-child as an argument and how it manages to iterate over the child elements.