Biaxial compressive strain has been used to markedly enhance the ferroelectric properties of BaTiO ₃ thin films. This strain, imposed by coherent epitaxy, can result in a ferroelectric transition temperature nearly 500°C higher and a remanent polarization at least 250% higher than bulk BaTiO ₃ single crystals. This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.