Food productsfood products are a rich nutrient source that will attract both bacterial and fungal colonizers. Food spoilagefood spoilage is a major threat for our food stock and is responsible for enormous losses worldwide, which makes it a research area that is very relevant with respect to the increasing demand on food during the next decennia. This chapter will highlight fungal spoilage dealing mostly with plant-based food products. At first, the relationship between the living crop and fungi will be illustrated. Between host and pathogen there exists a surprisingly complex communication and successful intervention may result in novel strategies to prevent post-harvest diseasespost-harvest diseases. Then the association of fungi with different types of processed foodprocessed food will be described. In time, different preservation techniquespreservation techniques are developed with the aim to discourage fungal development in the food product. These include fermentationfermentation, addition of salts or high concentrations of sugars, pickling, drying, cooling, the addition of preservatives, or a heating treatment before packaging. Only fungi that can survive these adverse conditions can successfully spoil processed food. Different aspects of stress resistance are addressed in this chapter including osmo- and xerotolerance, protective compounds inside cells, and heat-resistant structures. Food parameters are often surprisingly restrictive to the spectrum of fungal species which are able to grow and thus spoil the individual food types. Normally, less than ten and often one to three species are responsible for spoilage. Careful elucidation of the specific aspects of food spoilage may lead to novel tailor-made methods to decrease the enormous portion of our food that is lost.