The scientific work of the IUCr is conducted primarily through its Commissions. Each Commission comprises a group of scientists who report to the Executive Committee on a particular subject area. Individual Commissions are free to undertake or direct research activities that fall within their area of expertise, and a number have done so. Often these activities include the construction and maintenance of websites that are used by the scientific community active in that field. Follow the link below for the formal descriptions of the Commissions maintained by the IUCr Executive Secretary (including details of each Commission's terms of reference, membership and annual reports), or use the links in the menu to the community websites maintained by individual Commissions.