Traditional scientific policy advice used to happen behind closed doors in advisory bodies as a dialogue between scientists and policy-makers. The respective models for the interaction are basic linear arrangements assigning clear roles and primacy to one of the sides. However, these processes have been opened up following public pressure for more participation and deliberative decision-making models. Today, increasingly complex policy-decisions, like the assessment of climate change and the necessary actions to be taken, require more scientific input. At the same time, the medialization of politics and science has led to an intensified, more diverse multi- actor communication landscape. Correspondingly, also science communication does not happen in an isolated sphere, but takes place in the middle of political and societal debates - science communication is seen by some as political communication. The questions presented here are not new, but still intensely debated: What constitutes neutral science communication or policy advice and what partisan advocacy? Can so-called “scientific facts” and values be separated from each other at all? To which degree should scientists actively advocate for policy-decisions - or should they not do so? While the discussion is primarily led normatively, empirical evidence on the effects of scientific advocacy on citizens and on politicians is sparse and not painting a clear picture in this respect. This article portrays the development of the science- policy nexus and presents an overview on empirical research and the different perspectives on science advice and advocacy.