Initiatives to promote Open Science play a key role in the cultural shift toward an open research culture: they put the topic on the agenda of researchers and organize events and workshops. We present three initiatives at the University of Graz that pursue different approaches: the Graz Open Science Initiative as a collaboration of local researchers, the Arqus Open Science Ambassador Network as an international working group within the Arqus University Alliance, and university-level initiatives at the Department of Psychology. We summarize the challenges these initiatives face and highlight the successes they have achieved in promoting Open Science.