The U.S. Army Construction Engineering Research Laboratory, in partnership with the Composite Institute of the Society of Plastics Industry, Inc. and in support of the Army's facility seismic rehabilitation efforts, is investigating the applicability of fiber reinforced polymer (FRP) composite materials systems to strengthen unreinforced masonry (URM) walls. The end product of the research will be the design guidance and construction specifications necessary for the Army to use these materials systems. Much of the Army's inventory of facilities are usually either lightly reinforced or unreinforced. This structural system has been shown to perform poorly in past earthquakes and requires upgrading to ensure safety and mission operation during and after an earthquake. This research will develop procedures for the rehabilitation and/or upgrade of masonry walls using typical advanced composite materials systems. New 4-ft by 4-ft double width brick walls with FRP composite reinforcing applied to one face were constructed and will be tested. The shear performance of different widths and thicknesses of FRP composite applied across brick mortar joints of brick triplets, three brick high prisms with the center brick offset by half an inch, was also tested. Using FRP composites for seismic rehabilitation of URM walls show great potential. Triplet tests showed consistent strengthening of the mortar joints as a function of the width of the FRP composite overlay. With multiple layers of FRP applied, the shear strength of the mortar joints increased sufficiently to cause failure to occur via brick compression failures instead of via shear failure at the mortar joints.