Nitinol, a nickel-titanium alloy, exhibits the unique property of undergoing a temperature-dependent phase transformation. Associated with this phase transformation is a significant shape change that has led to the common designation of “memory material.” This shape change has been utilized to design mechanical fasteners which expand radially on transformation to produce interference fits for increased fatigue life components, give effective length reductions for high clamp-up forces, and form a rivet tail for low-cost installation. Various design concepts, manufacturing techniques, and mechanical properties are discussed.