Regulatory Guidance Letters (RGLs) were developed by the Corps as a system to organize and track written guidance issued to its field agencies. RGL’s are normally issued as a result of evolving policy; judicial decisions and changes to the Corps regulations or another agency’s regulations which affect the permit program. RGL’s are used only to interpret or clarify existing Regulatory Program policy, but do provide mandatory guidance to the Corps district offices. RGL’s are sequentially numbered and expire on a specified date. However, unless superseded by specific provisions of subsequently issued regulations or RGL’s, the guidance provided in RGL’s generally remains valid after the expiration date. The Corps incorporates most of the guidance provided by RGL’s whenever it revises its permit regulations.