The Q3s dummy is a three year old child crash dummy optimized for side impact crash testing. The dummy is built on the platform of the standard Q3 dummy that is part of the Q-series of child dummies developed in Europe to replace the P-series. Enhanced lateral biofidelity, durability and additional measurement channels have been designed into the Q3s dummy. The dummy features a new head that eliminates previously reported high frequency noise, an extensible neck that combines improved frontal flexion performance with the lateral and tensile performance of the Q series necks, a highly deformable shoulder with shoulder deflection measurement, a new arm with improved flesh characteristics, a laterally compliant chest and a pelvis with improved upper leg flesh, floating hip cups, and pubic load transducer. Biofidelity performance for the lateral 3 year old ATD is validated against the scaled biofidelity targets published by Irwin et al. (2002) This paper will describe the construction of the dummy and the laboratory biofidelity performance