Toxic cyanobacteria are increasingly being perceived as a potential health hazard, particularly in waters used for recreation. A few countries are developing regulations to protect human health from these toxins, and the World Health Organization (WHO) has published both a guideline value for one cyanotoxin in drinking water and a procedural guideline for recreational waters. This article presents an overview of the currently known cyanotoxins and of documented cases of human illnesses attributed to them. It further discusses exposure pathways and approaches to risk management. In this context, the WHO guideline for recreational waters is presented, and monitoring approaches are outlined.