Ab initio nuclear structure calculations with transformed realistic interactions

We discuss three elements of modern ab initio nuclear structure theory with an emphasis on the role of correlations in the nuclear many-body problem. Starting from the QCD-motivated construction of a realistic nuclear interaction we review two methods to derive phase-shift equivalent tamed interactions, the Unitary Correlation Operator Method and the Similarity Renormalization Group. Eventually we use these interactions for ab initio calculations within the importance truncated no-core shell model.