Heusler compounds, in both cubic and hexagonal polymorphs, are a ripe platform for engineering emergent electronic, magnetic, topological, and ferroic properties at crystalline interfaces. In these applications, the ability to control interfaces with near atomic level control is of tantamount importance; however, challenges such as interdiffusion have hampered their development. Here, I will discuss our efforts to control the properties of Heusler interfaces using precision growth by molecular beam epitaxy (MBE). I will focus on the following topics: (1) the use of epitaxial strain to stabilize the hexagonal phase of several polar metal and ferroelectric candidates, (2) the use of monolayer graphene diffusion barriers for enhanced atomic ordering across interfaces, and (3) the phase segregation of ferromagnetic nanostructures from a semiconducting FeVSb matrix with coherent epitaxial interfaces. Together, these examples illustrate the power of epitaxy and interfaces in controlling the properties of Heuslers and other intermetallic compounds.