Leptomonas is a genus of parasitic flagellate protist belonging to family Trypanosomatidae and subfamily Leishmaniinae <small>sensu Maslov & Lukeà ¡ 2012</small>. It is a monoxenous parasite of mainly Hemiptera, Diptera, and Siphonaptera insects.
In addition to Leptomonas, one-host trypanosomatids from insects have been traditionally placed in genera Crithidia, Blastocrithidia, Herpetomonas, Rhynchoidomonas, and Wallaceina.
The etymology of the genus name Leptomonas derives from the two Ancient Greek words (), meaning "fine-grained, tiny", and (), meaning "alone, isolated" (as an adjective), or "a unit" (as a name).
There are 18 species of Leptomonas.