Transcription of protein-coding genes governs organism development, cell differentiation, and cell identity. We had previously provided the mechanisms of transcription initiation and elongation by RNA polymerase II, but these studies were carried out on naked DNA, not on the natural template, which is chromatin. With the ERC Advanced Grant project CHROMATRANS we were able to elucidate transcription initiation and elongation in a chromatin context on a structural level. In particular, we obtained three-dimensional structures of the RNA polymerase II pre-initiation complex on a nucleosome and several structures of RNA polymerase II elongation complexes transcribing a nucleosome. Since several functional states were trapped and several different factors were present in these structures, we could combine them into a movie of the polymerase passing through a nucleosome that now includes also the backtracking, arrest and reactivation of polymerase during this process. These studies provide a basis for chromatin transcription and its regulation by cellular cues. Several junior researchers could base their career on these studies and have taken principal investigator positions within Europe, the USA and Asia.