The International Yngling Class Rules are issued by World Sailing. The International Yngling Association (IYA) can make proposals to World Sailing (WS) on changes to the Class Rules that it may find necessary. The latest issue of the Class Rules can be found on the WS's website.
http://www.sailing.org/classesandequipment/YNG.php
The latest version of the rules can be found under the technical tab.
The WS site also contains some history and special interpretations.
If you have any questions about the Rules and their meaning please contact any of the IYA Yngling Measurers.