Sand flies (Diptera: Psychodidae: Phlebotominae) are the only proven vectors of leishmaniasis. Leishmania parasites develop and differentiate in the sand fly gut where they reside alongside the vector's gut bacteria. Gut bacteria are important to sand fly's nutrition, oviposition, and defence against pathogens. In vectors, gut bacteria also influence vector competence. However, the link between specific bacterial taxa and sand fly vector susceptibility is poorly documented. In this review, we investigated current published data on bacterial communities in sand flies and provide a better understanding of how gut bacteria influence sand fly-Leishmania interactions. Understanding sand fly-bacteria-Leishmania interactions will provide new targets in vector control and Leishmania-transmission blocking approaches.