Silages constitute a component of dairy and beef rations worldwide. They are required to fulfill the demands of both the animal and the ultimate consumer of animal products, particularly with respect to safety. Silage is susceptible to the introduction of hazards throughout the entire production chain, from field to feed. Ensiled forages may contain various mycotoxins, stemming from preharvest contamination by Fusarium and Aspergillus species and/or from postharvest contamination by toxigenic molds, such as Aspergillus and Penicillium. Silage has also been detected to be contaminated with a diverse range of pathogens and chemical hazards. Most of these hazards are associated with poorly fermented silages, which can be avoided by enhancing lactic acid fermentation and preventing aerobic deterioration. This chapter summarizes types, prevalence, and levels of mycotoxins, chemical hazards, and pathogens in ensiled forages, describes their detrimental impacts on the health of ruminants, and outlines effective prevention and mitigation strategies.