The microbiota ecosystem is an important determinant of human health. Recent findings suggest several connections between microbiome composition and the onset and treatment of certain diseases. The following paper presents a summary of available information on principles of microbiota composition, its relation to the immune system, and possible implications for the healthcare process. Recent findings in microbiology suggest that the composition of the human microbiome has a significant effect on an individual’s state of health. More importantly, it has been determined that microbiome composition varies depending on several factors, including geographical location and the functions of a body part. Therefore, it would be logical to suggest that individual and group differences in microbiome composition determine the effects of microbiota on human health. The first factor that is considered responsible for the observed differences in the functional properties of the site where the microbiota proliferates. For example, the composition of a bacterial community within a microbiome occurring in the oral cavity is expected to be relatively similar in different individuals (Clemente et al. 1258). However, it is also evident that despite the similarities, communities in different hosts display significant inter-individual variability. While some of the differences can be attributed solely to individual parameters, certain demographic factors are also known to influence the outcome. For instance, the microbiome found in infants differs significantly from that occurring in adults (Dave et al. 249). In a similar manner, gender differences are also associated with a certain amount of variety in microbiome composition. On a larger scale, human groups such as populations of a certain ethnicity may harbor a microbiome with a unique set of characteristics. The most apparent explanation for the phenomenon is the involvement of genetic variables, which would also account for the differences between individuals within a given ethnic group. Several researchers point to the fact that microbiota from related individuals living in the same environment features more similarities than those found in unrelated people, confirming the assumption (Goodrich et al. 789). However, it is also reasonable to consider environmental factors as responsible for at least some of the similarities. The factors that affect differences in community microbiome composition can be divided into two categories. The first category focuses on environmental factors and includes diet, gastrointestinal infections, smoking, and the effects of medications, with antibiotics having a major impact on community microbiome composition. It should be pointed out that the environmental factors that likely affect the microbiome are numerous, complex, and, as a result, difficult to control. For this reason, the available findings are inconclusive. Nevertheless, it has been established that only 10% of the microbiota remains unchanged over a long period of time, which suggests that the majority of changes are determined by external influences (Dave et al. 250). The second category includes genetic factors and determines the differences within populations belonging to the same ethnic group. Limited evidence exists that the