In my talk I will attempt to provide an overview on the application of the density matrix renormalization group (DMRG) algorithm in quantum chemistry. I will compare to traditional approaches with respect to limitations and capabilities. I will highlight the ma- trix product operator structure of our second-generation DMRG program and discuss its features. Emphasis will be put on how orbital-entanglement measures can be exploited to automatically select proper active orbital spaces, a major problem of all multi-configurational approaches.