The working group on marine diseases will bring together researchers working with diverse diseases of marine organisms with theoreticians and statisticians. Epidemiological studies of diseases in marine systems have been rare and there is a paucity of information regarding even the most basic properties of marine pathogens (e.g. identity, host-specificity) and factors (e.g. environmental correlates) affecting disease processes (Harvell et al. 1999). In particular, little is known about the mechanisms of either disease transmission or host resistance and their roles in facilitating disease outbreaks. Although theoretical and experimental practices developed to model infectious disease in humans (Anderson & May 1991),wildlife (Daszak et al. 2000) and agricultural systems (Real 1996) have provided some useful insight, the applicability of these "terrestrial" models to comparatively more open system like the ocean is not known. Moreover, knowledge of mechanisms of host resistance among marine invertebrates is effectively a black box; we lack understanding of basic disease resistance mechanisms and their interaction with environmental stressors. Using a few well studied host-pathogen interactions or those with long-term monitoring data, we will 1) synthesize what is currently know about marine diseases and their environmental drivers, 2) develop new epidemiological theory for analysis of marine diseases, and 3) review differences between disease ecology in marine and terrestrial habitats, including the consequences of spill-over of infectious micro-organisms from farmed into wild populations. collapse