Prebiotics have been established as a series of feed compounds that serve as specific substrates for gastrointestinal tract (GIT) bacteria. The general premise is that such compounds support GIT bacteria that benefit the host. In addition, GIT bacteria supported by prebiotics can be antagonistic to foodborne pathogens and prevent their colonization in the GIT. In poultry, prebiotics have been used primarily to prevent the establishment of foodborne pathogens but have also received attention regarding their impact on overall GIT health. This chapter reviews the impact of prebiotics on bird health, GIT function, and prevention of foodborne pathogen GIT colonization. Following an introduction, prebiotics are defined and discussed. Then follows an overview of the potential impact of such prebiotics on avian upper GIT health. A section is included on the avian intestinal microbiome, function, and prebiotics. The characteristics of the avian cecum are presented in detail, including coverage of the cecal microbiome and the use of prebiotics.