It depends, but in general there is a time limit on classification. http://en.wikipedia.org/wiki/Declassification#United_States http://en.wikipedia.org/wiki/De

It depends, but in general there is a time limit on classification. http://en.wikipedia.org/wiki/Declassification#United_States http://en.wikipedia.org/wiki/Declassification#United_States explains it pretty well, and http://en.wikisource.org/wiki/Executive_Order_13526 http://en.wikisource.org/wiki/Executive_Order_13526 is the executive order that governs the classification system used by the US Government.