Complex oxide materials possess a range of interesting properties and phenomena that make them candidates for next-generation devices and applications. But before these materials can be integrated into state-of-the-art devices, it is important to understand how to control and engineer the response of these materials in a deterministic manner. In this talk we will discuss the science and engineering of thin-film versions of these materials. We will explore the role of the epitaxial thin-film growth process and the use new types of lattice mismatch strain to engineer a range of systems with special attention to ferroelectric materials. In recent years, the use of epitaxial strain has enabled the production of model versions of these complicated materials and the subsequent deterministic study of field-dependent response. Here, we will investigate how new manifestations of epitaxial constraint can enhance electric field, stress, and temperature susceptibilities (i.e., dielectric, piezoelectric, pyroelectric, and electrocaloric effects) in ferroelectrics. In particular, we will explore a number of routes to push the boundaries of modern thin-film strain to control materials including (but not limited to): 1) the production and use of strain gradients in compositionally-graded materials, 2) the use of film orientation to produce exotic domain structures and responses, and 3) superlattice routes to produce novel states of matter. The discussion will range from the development of a fundamental understanding of the physics that lies at the heart of the observed effects, to an illustration of routes to manipulate and control these effects, to the demonstration of solid-state devices based on these materials.