How uncertainty data is visualised can play a significant role in analysis and decision-making, especially involving multiple stakeholders. Even when only one person is responsible for every aspect of analysis and decision-making, visualisation may still play a significant role in how uncertainty is understood--i.e. in how the decision-maker 'communicates uncertainty to themselves.' Using the right visualisation tools can have a positive impact on decision quality. But this positive impact should never be taken for granted: visualisations can also have unexpected side-effects, and there is the risk that they can be misinterpreted or otherwise misused. This primer, published by the Analysis under Uncertainty for Decision-Making network (AU4DM), summarises the current state of the art of uncertainty visualisation research. It brings together a wealth of relevant studies, concepts, and practical tools and recommendations. It also represents research-in-progress: an open invitation for researchers in visualisation, decision analysis, psychology, and other fields to share their findings and to contribute to future editions.