This World Health Organization document evaluates the potential of climate-based disease early warning as a means of improving preparedness for, and response to, epidemics. The authors develop a conceptual framework for constructing and evaluating a climate-based early warning system (EWS). The report highlights that many of the most important infectious diseases, and particularly those transmitted by insects, are highly sensitive to climate variations. However, the published literature includes no full descriptions of climate-based EWS being used to influence disease control decisions. This is partly because affordable and accessible data and analytical tools have only recently become widespread and as of yet, there is no common consensus on good practice in building predictive models.The report concludes that climate information can be used to improve epidemic prediction, and therefore has the potential to improve disease control. It is important to maintain and strengthen disease surveillance systems for monitoring the incidence of epidemic diseases and to clarify definitions of terminology and methods for assessing predictive accuracy.