Aims: To review studies examining the appendiceal microbiota and microbial changes in acute appendicitis. Methods: After a systematic literature search, 11 studies examining the appendiceal microbiota (414 samples) using non-culture-based methods were included. Results: The appendiceal microbiota showed decreased α-diversity compared with fecal microbiota. Inflamed and uninflamed appendices showed differences in β-diversity, and there was an increased abundance of oral-associated bacteria in inflamed versus uninflamed appendices. Conclusion: The appendiceal microbiota exhibits lower α-diversity than the fecal microbiota, with an increased abundance of oral-associated bacteria. Compared with uninflamed appendices, the appendix microbiota in acute appendicitis also showed increased abundance of oral-associated bacteria, but no bacterial profile unique to either complicated or uncomplicated appendicitis was found. Plain language summary: This article represents a summary of the current literature examining the bacteria in the human appendix.We aimed to describe the bacterial community in the appendix and look for evidence of bacterial differences between diseased and healthy appendices, as well as evidence of bacteria being the cause of acute appendicitis. We found that the bacteria in the appendix are different from the bacteria in stool. Furthermore, bacteria are different when comparing diseased and healthy appendices. The diseased appendix had more types of bacteria that are normally found in the mouth than the healthy appendix. Our summary did not find any evidence that bacteria are the main cause of developing acute appendicitis. Tweetable abstract: This review found a lower ?-diversity of the appendiceal microbiota compared with the fecal microbiota and an increased presence of bacteria commonly found in the oral cavity in the appendix. Acute appendicitis is characterized by an altered microbiota with increased abundance of Fusobacteria.