The Institute was officially established as an association under Dutch law in 2007. Before that, the Institute was part of the International Astronautical Federation, which founded it in 1960. The Statutes and Bylaws of the IISL are adopted by the General Assembly of members which meets each year during the International Astronautical Congress.
In 2013, the Statutes were amended after a lengthy review process which included a survey among all members. The Bylaws were amended several times by the General Assembly.
The current version of both documents can be downloaded here.