Models represent very powerful tools to improve forecasting, decision-making, and planning of agricultural activities. They play an increasing role in the context of climate change adaptation supporting the identification and evaluation of short- and long-term strategies. This chapter introduces approaches to modeling for two groups—pests (including arthropods and to a lesser extent weeds) and diseases—using agrometeorological data for crop protection. For each group, it also introduces modeling concepts and analytical approaches to modeling before discussing more complex simulation models. The chapter discusses atmospheric transport models. For pest and disease models, it addresses the requirements in terms of data, information technology, model design, requirement, and validation. The chapter describes the main products, delivery methods, and the expected benefits for the different categories of stakeholders. Finally, it provides an overview of future developments in the field of pest modeling. ILCYM.