The guidelines were first established in 1989 by the International Committee of the Corpus Vitrearum for the Conservation of Stained Glass in association with the International Scientific Committee for Stained Glass of ICOMOS. 

These guidelines , written in 2004, outline the ethical principles underlying the conservation and restoration of stained glass of all periods. They serve as a reference for conservators/restorers and consultants, as well as an introduction and source of information for individuals and organizations responsible for the preservation of stained glass.The original versions of the current edition are in English, French, and German. 

The full text is available here in several languages:

French (PDF)

English (PDF)

German (PDF)

Dutch (PDF)