FAIR Open Data is one of the pillars of modern research. It is the paradigm whereby data ultimately become available and findable without restrictions, independently of the circumstances of their acquisition, thus sparking the generation of more science results and allowing the scrutiny of previous claims. Virtually all of today's facilities are equipped for Open Data, and practically all current funding schemes require it in some form.

ESO has a long tradition in Open Data, having run a science archive since the late 1980s. In this Informal Discussion, we will review the theory, practice, perils and impact of Open Data, using the ESO Science Archive, and beyond, as guidance.