Ferroelectricity at the nanoscale has emerged as fertile ground for new physical phenomena and devices. The advance in oxide thin film technology has allowed growth of nanoscale oxide ultrathin films and heterostructures with extremely high structural quality. As an example, I will present the results on nanoscale BaTiO₃/SrTiO₃ superlattices and ultrathin BaTiO₃ films. In bulk, BaTiO₃ is ferroelectric below 403 K and SrTiO₃ is quantum paraelectric. Using ultraviolet Raman spectroscopy we showed that one-unit-cell-thick BaTiO₃ layers in BaTiO₃/SrTiO₃ superlattices are not only ferroelectric (with T_c as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO₃ layers adjacent to them. T_c was tuned by ~500 kelvin by varying the thicknesses of the BaTiO₃ and SrTiO₃ layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.