Ferroelectrics, which are materials that host an electrical polarization that can be reversed by an applied electric field, are of enduring fundamental scientific interest and have numerous electronic, sensing, and energy applications. In this talk, I will highlight two examples of how first-principles calculations can reveal new functionalities in ferroelectric oxides. First, I will discuss isolated magnetic dopants in ferroelectric oxides as a platform for electric-field control of single spins. Our density functional theory (DFT) calculations reveal that a magnetic dopant’s magnetocrystalline anisotropy energy, and hence its preferred spin orientation, is highly tunable through changes to ferroelectric structural distortions. Second, I will present our discovery of an unusual electric auxetic effect in several families of ferroelectric layered perovskites, in which polarization increases under both longitudinal and transverse applied stress. This unconventional electromechanical behavior offers a pathway towards designing large hydrostatic piezoelectric responses, which are of interest for underwater sensing applications. I also will comment on some of our future research directions arising from these works.