**Abstract**

Muscularis macrophages are a newly discovered population of macrophages distributed within the smooth muscle layers of the gastrointestinal tract. Muscularis macrophages are emerging as essential cell keepers of homeostatic gastrointestinal function, and when affected, can lead to functional gastrointestinal disorders. In this chapter, we briefly introduce the phenotype, the distribution of muscularis macrophages, and the difference compared with other tissue-resident macrophages. We next describe how they contribute to normal gastrointestinal function by interacting with cells required for gastrointestinal motility, such as enteric neurons. Finally, we highlight the increasing pieces of evidence suggesting the contribution of muscularis macrophages to gastrointestinal function diseases, such as gastrointestinal inflammation, gastroparesis and post operative ileus.

**Keywords:** macrophages, muscularis propria, gastrointestinal tract, enteric neurons, gastrointestinal motility
