Optimal gut health is of vital importance to the performance of commercial poultry production. There is a direct relationship between bird performance and a “healthy” intestinal tract, with the gut responsible for regulating physiological homeostasis that provides the animal the ability to withstand infectious and non-infectious stressors. Gut health encompasses a number of physiological and functional features, including nutrient digestion and absorption, host metabolism and energy generation, a stable microbiome, mucus layer development, barrier function, and mucosal immune responses all of which are required to interact together so that the bird is able to perform its physiological functions to perform as close to 100% of its genetic potential. Comprehension of gut health requires the elucidation of the interactions between all of these components. Understanding the interactions between these diverse physiological features emphasizes the extent of areas encompassed by gut health and the ability to regulate poultry production. Thus, understanding gut health has been a primary focus of the poultry industry worldwide as a means of increasing production of meat and eggs, reducing the use of antibiotics, and enhancing animal welfare.