In thin films, new phases can be encountered near interfaces, whether it is the substrate-film interface or subsequent interfaces in the case of heterostructures. Both structural properties and surface morphology are a direct result of the thin film growth, controlled by deposition conditions and substrate properties, which in turn influence the electrical properties and determine their applicability in multilayer structures. At the initial growth stage, the stacking sequence of the individual atomic layers at the interface with the substrate is influenced by the substrate surface properties. During subsequent deposition, the lattice mismatch between substrate and growing film becomes dominant. In this article, an overview is given of the complex growth mechanisms of YBa2Cu3O7-δ on SrTiO3 substrates. The afore mentioned issues will be addressed, with a focus on initial growth, interface engineering and strain, leading to phases that are different from the bulk both structurally and in their superconducting properties.