Epidemics pose a major risk not only to humanity, but also wild animal and plant populations. To maintain global food security, biodiversity and human health, we require better ways of forecasting disease outbreaks in an era of broad environmental change. Previous research has focussed on assessing the size of individual epidemics for a given host-parasite interaction. However, in many cases, host populations experience repeated epidemics that vary in size and severity over time and there are certain characteristics shared between different types of host-parasite systems. Therefore, I propose a simple conceptual model, called the ‘Disease Cycle’, that links the size of past and future epidemics within the dynamic context of a changing environment. In this review, I summarise some of the past research relevant to the Disease Cycle and consider how environmentally mediated host and parasite selection and changes in population genetic diversity could influence future epidemics. I also highlight areas of the Disease Cycle that are in need of further study. Overall, I find strong evidence for certain links in the Disease Cycle, but there some knowledge gaps, such as the relationship between epidemic size and the strength of antagonistic selection, that need to be filled. My hope is that this Disease Cycle concept can help the scientific community embrace epidemics as recurrent events, improve forecasts of future disease outbreaks and aid in the development of control strategies for the management of infectious diseases.