While all the guides shown in the link that David gave are registered, not all registered guides are on that list. For instance, I only recently sent in my details to be listed there. There's another list available at http://www.tour-guides.co.il/search.php (enter a name in the box marked "name" and click the "search" button). It's supposed to be only members of the Israel Tour Guides Association, but while I'm not an ITGA member but appear on that list, I know other guides who ARE members who are not found on that list.
So - let's say the person you are considering hiring to guide you in Israel is not show on either of these lists but insists he/she is licensed - how do you know? Well, you can ask for his/her full name and Official Israeli Guide License Number and then you can write to info@goisrael.org.il - give the name and license number of the guide and simply ask the Ministry of Tourism for help!
Hope that works for you and others!
suzanne
suzanne pomeranz
SuzTours: Every Day an Adventure!
jerusalem, israel
suztours@gmail.comhttp://suztours.blogspot.com