The development of active materials with properties for enhancing the shelf-life and safety of packaged food is nowadays one of the most challenging research activities. Due to the aerobic nature of fungal metabolism, many industrial applications for preserving food from mold spoilage are concerned with the use of modified-atmosphere packaging (MAP). This chapter provides comprehensive illustrations of low oxygen and high carbon dioxide partial pressure effects on a wide range of fungal species. Many tables are presented to report and compare the effects of oxygen and carbon dioxide on mold development as a function of environmental factors such as temperature and water activity. In addition, a short section is dedicated to discussing the potential of MAP to reduce mycotoxin production. A comprehensive analysis of the numerous studies cited is difficult, due to the variety of approaches used. Under some experimental conditions, undesirable stimulation of the metabolism is pointed out in certain fungal species. Nonetheless, oxygen decrease, carbon dioxide increase, and combinations of both are more often reported to have a fungistatic effect. In addition to synergistic effects, control of environmental factors that affect both gases' solubility and diffusivity in growth matrices can significantly improve MAP efficacy. This review underlines the relevance of the inclusion of MAP, as far as possible, in the hurdle technology concept in order to improve the quality and safety of food products.