Perovskites can be deposited as epitaxial thin films on top of other perovskites, using techniques such as pulsed laser deposition and molecular-beam epitaxy. These films can be a couple of nanometres thick or as small as a single unit cell. The well-defined and unique structures at the interfaces between the film and substrate can be used for interface engineering, where new types properties can arise. This can happen through several mechanisms, from mismatch strain between the substrate and film, change in the oxygen octahedral rotation, compositional changes, and quantum confinement. An example of this is LaAlO grown on SrTiO, where the interface can exhibit conductivity, even though both LaAlO and SrTiO are non-conductive. Another example is SrTiO grown on LSAT ((LaAlO) (SrAlTaO)) or DyScO can morph the incipient ferroelectric into a ferroelectric at room temperature through the means of epitaxially applied biaxial strain. The lattice mismatch of GdScO to SrTiO (+1.0%) applies tensile stress resulting in a decrease of the out-of-plane lattice constant of SrTiO, compared to LSAT (−0.9 %), which epitaxially applies compressive stress leading to an extension of the out-of-plane lattice constant of SrTiO (and subsequent increase of the in-plane lattice constant).