The grand challenge of modern condensed matter physics is to achieve a unified understanding of strongly correlated oxide systems. Apart from the intellectual challenge, these systems are the most promising hunting ground for new device concepts and technology and, therefore, we also need to have control on their wide array of properties. Here we present examples of controlling oxide properties of three major correlated oxide classes: ruthenates, manganites and cuprates, probed by a combination of advanced spectroscopy and microscopy experimental techniques. We tuned the properties of bi-layered ruthenium oxide by introducing dilute Mn impurities and studied the interplay of host-impurity electronic states. Manganite bulk and interfaces are studied, focussing on the role of competing orders and influence of substrate on the interfacial magnetism. Cuprate high Tc superconductor YBCO is explored by doping the electronically reconstructed polar surfaces via surface impurities. These studies reveal the enormous flexibility of oxide systems to internal and external perturbations and point to future research opportunities.