The 4th VAMAS TWA 20 Workshop, hosted by the NIST Center for Neutron Research (NCNR), was held from April 22–24.1998 inGaithersburg, Maryland. VAMAS TWA 20 is a Technical Working Area within the international Versailles Project on Advanced Materials and Standards. The focus of TWA 20 is residual stress measurement by neutron diffraction. The scope of TWA 20 and discussions held at its inaugural meeting in January 1996 at the ILL in Grenoble, France were summarized by the chairman of the organization, G.A. Webster, in a meeting report in Neutron News Vol. 7, No. 4, 1996. Featuring discussions and presentations by the leaders of the five task groups, the present workshop focused on reviewing the actions and progress that had been made since the Nyköping meeting (June 1997) and the tasks to be carried out over the next several months. A few hours of the meeting were devoted to a tour of the neutron facilities at the NCNR.