The development of bright mid-infrared and THz laser sources, capable of resonantly exciting phonons in crystals, has created new opportunities for the control of functional properties with external fields, namely light. One such mechanism involves resonantly exciting infrared(IR)-active phonons of the crystal to large amplitude, which interact with other phonons via anharmonic coupling. In these so-called nonlinear phononics experiments, the light pulse can induce a transition to a metastable phase with properties that are either difficult or impossible to access in the equilibrium structure. In this dissertation, I explore the ultrafast control of functional properties in perovskite oxides with light, using theory, dynamical simulation, and first-principles calculations. In Chapter 1, I present the possibilities of ultrafast control of functional properties in materials and a historical perspective of nonlinear phononics. In Chapter 2, I cover the essential concepts necessary to understand the rest of the chapters, namely: phonons, a figure of merit for nonlinear phononics model, and density functional theory. In Chapter 3, I apply the figure of merit from Chapter 2 to the perovskite LaAlO3, by calculating all IR/Raman couplings and show how the predicted Raman displacement varies with hydrostatic pressure. In Chapter 4, I show that the nonlinear phononics model allows for IR/strain coupling, with good agreement with data from experimental collaborators who measured the effect in epitaxially strained LaAlO3. I also cover my computational explorations of epitaxial strained Ca2RuO4, again featuring experimental collaboration. In Chapter 5, I use the nonlinear phononics model to explain recent experimental evidence of light induced ferroelectricity in SrTiO3. I then show, based on computational results, that epitaxial strain can be leveraged to enhance the effect. Finally in Chapter 6, I show that the conventional nonlinear phononics mechanism is a consequence of a more general framework involving biquadratic coupling. This biquadratic coupling allows for coupling between IR phonons at zone-center to modes at arbitrary wave vector. I show that phonons at the zone-edge of KTaO3, which has no Raman phonons and is always cubic in bulk, can be dynamically destabilized. The different possible dynamically induced regimes from the biquadratic coupling were condensed into a general phase diagram, which was developed with Floquet theory.