Stripe rust, caused by Puccinia striiformis, is a polycyclic disease and its epidemic is mainly dependent upon the disease development rate. Although the pathogen has a heteroecious macrocyclic lifecycle that consists of five spore stages, it almost completely reproduces asexually on its primary hosts of cereal crops and auxiliary hosts of wild grasses. The primary inoculum to cause epidemics on cereal crops is mainly from cereal crops, volunteer plants and grasses. Urediniospores can be disseminated by wind for long distance, and also can be carried on clothes and shoes for unintended introduction. The fungus can survive summer and/or winter as mycelium in host tissue for months and/or as viable urediniospores in the air or host surface for different length of time in different regions depending upon environmental conditions. Stripe rust epidemics are affected by various crop and environmental factors, especially host factors such as cultivar susceptibility and cropping systems, and weather factors such as moisture and temperature. Various models for predicting stripe rust have been developed in different regions of the world based on weather factors or the combination of weather factors and cultivar susceptibility. These models have different degrees of usefulness in the disease management.