Future sea-level change is characterized by two types of uncertainty: quantifiable uncertainty and unquantifiable ambiguity. Both types are relevant to long-term coastal planning, and communicating them effectively along the boundary chain that runs from research to adaptation policy and practice is a central challenge faced by sea-level scientists seeking to support decision-making. Scientific assessments – including both the global Intergovernmental Panel on Climate Change (IPCC) climate assessment and more targeted, regional sea-level assessments – play key roles in this chain. While assessments have taken diverse approaches to communicating sea-level projection uncertainty, literature evaluating these approaches is limited and unsystematic. Here, we review how past IPCC assessments communicated sea-level projection uncertainty and how this information has been interpreted by regional assessments, as well as alternative approaches used by recent subnational assessments and ways in which regional assessments and policy guidance simplify information for practical use. Building upon lessons from other assessments, the IPCC Sixth Assessment Report (AR6) communicates quantifiable uncertainty and ambiguity in key tables and figures with the goal of preserving both elements as projections are adapted for regional application.