Pure strontium titanate exhibits a cubic perovskite-type structure at room temperature. Many approaches to break this high degree of symmetry are accessible. The present review summarizes the possible methods by discussing the effects of ion implantation, temperature treatment and external electric fields. Since oxygen vacancies are the most prominent and most mobile defect species in strontium titanate, they play a major role also for structural changes due to external influences. Here, an overview on the involved microscopic models will be given.