Data visualizations are ubiquitous and critically important to generating new knowledge in several fields today. They often play a central role in different stages of the research process, from exploring data with visual analytical methods to communicating findings with visual displays aimed at both experts and general audiences. In this talk I will focus on the latter, visualizations used to communicate complex information. In this communicative role, visualizations are visual (re)presentations of results, requiring presentation skills originated in well-established practices, such as graphic design and journalism. Through case studies, I will examine cognitive and perceptual constraints, visual strategies and tradeoffs, and critically reflect on common challenges of the medium.