Despite being introduced in Europe nearly 20 years20 years ago, cross-laminated timber (CLT) is still not widely used in North America, and it has only recently garnered attention as a new construction material in the US. One primary reason for this is because of a lack design procedures for CLT as a lateral force resisting system for seismically active regions of the US. A CLT subassembly that has not been fully investigated is a horizontal diaphragm for floors, roofs, or bridge decks. The purpose of this study was to investigate CLT diaphragm behavior through a series of large-scale cyclic loading tests. A 5×4.27 m5×4.27 m (16 ft 5 in.×14 ft16 ft 5 in.×14 ft) CLT diaphragm was tested in a cantilever configuration in which the assembly was subjected to the Consortium Universities for Research in Earthquake Engineering (CUREE) (reversed cyclic) loading protocol applied under displacement control. These diaphragm tests illustrated the rigid behavior of the CLT panels and the ability of the shear connectors between CLT panels to dissipate energy. These tests highlighted possible failure mechanisms and the importance of chord strength on the CLT diaphragm load-deflection performance. The failure mechanism observed and load-deflection results from this experimental study provide information for the development of design procedures for CLT diaphragms.