After the first contact between host and pathogen, a series of specific events follow which leads to the development of a disease and, ultimately, an epidemic. This series of events is called a disease cycle. Often, a disease cycle is essentially the same as the pathogen's life cycle, but the key difference is that a disease cycle primarily describes the disease as it develops as a result of the interaction between the host plant and the pathogen. In the first section of the chapter, a series of terms describing what is essentially a continuum of lifestyles were explained; through commensal via mutualistic and pathogenic to saprophytic. There are two extremes of pathogenic lifestyle-biotrophic and necrotrophic. Pathogens that are purely biotrophic are usually obligate parasites, whereas necrotrophic pathogens can also survive as saprophytes.