Understanding materials systems at the nanoscale and how they give rise to their macroscale properties dictates the central mission of materials science and engineering. My Dissertation is focused on understanding the control and manipulation of ferroelectric polarization to produce new phenomena and to expand the utility of ferroelectric materials. While much work has been done on individual thin films of canonical ferroelectrics such as PbTiO3 and prototypical dielectric material SrTiO3, the demand for novel phenomena calls for a thorough understanding of their structure-property control in thin film form wherein structures, properties, and function well beyond those found in parent single composition films can be elicited by standard routes such as substrate-induced, strain-controlled pathways. The work herein is primarily based on the development of the Pb1-xSrxTiO3 epitaxial thin-film system as a new platform for investigating the behavior of ferroelectric polarization under different chemistries and heterostructure formats such as single-layer, multilayer, and superlattice geometries to elicit novel phenomena. First, using a combination of the Ginzburg-Landau-Devonshire thermodynamic models, phase-field simulations, epitaxial thin-film growth, and characterization, I probed the mixed-phase domain structure evolution in Pb1-xSrxTiO3 thin films, and its connection with Euler characteristics, thermal-annealing effects, and dielectric susceptibility. Therein, I observed that varying strontium content provides deterministic strain-driven control of hierarchical domain structures in Pb1-xSrxTiO3 solid-solution thin films wherein two types, c/a and a1/a2, of nanodomains can coexist. A relationship between the different mixed-phase domain patterns and their topological nature is established using the Euler characteristic. In turn, the dielectric properties were also measured, and it was found that the connected-labyrinth domain patterns exhibit the highest dielectric permittivity due to the highest shared interdomain perimeter. After exploring the mixed-phase domain architectures in the Pb1-xSrxTiO3 thin films, I studied the understudied area of in-plane polarized ferroelectrics. Interlayer coupling, such as exchange interactions at the interface between an antiferromagnet and a ferromagnet, can produce exotic phenomena that are not present in the parent materials in magnetic systems. There is considerably less work on analogous ferroelectric counterparts. Here, Pb1-xSrxTiO3 thin films showing purely in-plane polarized domains with different chemistries have been used to create exchange-interaction-like behavior in ferroelectrics and to generate multistate memory. In this work, electric or polarization analogs of such exchange interactions are reported, and their physical origins are explained for bilayers of in-plane polarized Pb1-xSrxTiO3 ferroelectrics. Further control over the strontium content and thickness of the layers provides for deterministic switching properties of the bilayer systems resulting in phenomena analogous to an exchange-spring interaction. Eventually, with the control of these interactions, multistate-memory function and lowering coercivity of high coercivity in-plane ferroelectrics was reported in in-plane bilayer geometries. Next, I explored the fully-ferroelectric (PbTiO3)n/(PbxSr1-xTiO3)n superlattice system wherein in-plane ferroelectric polarization in the PbxSr1-xTiO3 provides the appropriate boundary conditions for the formation of the ferroelectric polar vortices. These superlattices exhibit substantially enhanced piezoelectric and ferroelectric responses in the out-of-plane direction, which arises from the ability of the polarization in both layers to rotate in the out-of-plane direction under the field. In the in-plane direction, the layers are found to be strongly coupled during switching, and in heterostructures with (PbTiO3)n/(SrTiO3)n ferroelectric-dielectric building blocks, it is possible to produce multistate switching and polarization stability. This research further expands the realm of systems able to support emergent dipolar texture formation, and it does so with entirely ferroelectric materials, thus greatly improving their response to applied fields. Lastly, I investigated the potential of BaTiO3 ferroelectric thin films for low-voltage operation for ferroelectric field effect transistors (FEFET) applications. In this work, ultrathin SrRuO3 is used as channel material. Herein, I showed significant channel resistance modulation as a function of applied gate voltage in the low-voltage regime. This work demonstrates a potential route towards the inclusion of low coercive field ferroelectric materials in FEFET applications for future generation fully oxide devices. Overall, my work presented in this Dissertation provides new insights into understanding the fundamental mechanisms of emergent ferroelectric properties and demonstrates new routes to engineering domain structures for the enhanced dielectric response, exotic in-plane polarization switching in ferroelectric bilayer thin films, polar textures generation in superlattices, and usage of low coercivity material for FEFET applications.