A large variety of transport properties have been observed at the interface between the insulating oxides SrTiO3 and LaAlO3 such as insulation, 2D interface metallicity, 3D bulk metallicity, magnetic scattering, and superconductivity. The relation between the structure and the properties of the SrTiO3/LaAlO3 interface can be explained in a meaningful way by taking into account the relative contribution of three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. The emerging phase diagram is much richer than for related bulk oxides due to the occurrence of interface electronic reconstruction. The observation of this interface phenomenon is a display of recent advances in thin film deposition and characterization techniques, and provides an extension to the range of exceptional electronic properties of complex oxides. The interface between the insulating oxides SrTiO3 and LaAlO3 shows a variety of transport properties. The properties of the interface can be explained by three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. Irrespective of the origin of mobile charge at these heterointerfaces, once harnessed and controlled all could lead to heterostructures, where the properties are determined by strong correlation effects, and therefore full of surprises.