**Abstract**

According to WHO, Leishmaniasis is a complex neglected disease caused by a protozoa parasite from over 20 Leishmania species transmitted by more than 90 sandfly species, showing three main forms: visceral, cutaneous, and mucocutaneous. The efficient prevention and control of leishmaniasis are very difficult to achieve, depending on the combination of different intervention strategies, usually resulting in failure. Additionally, the correct diagnostics require the combination of clinical signs with laboratory tests, and only a few therapeutical options are available for patients. To improve this scenario, greater efforts in research for control and treatment are needed. For this purpose, the study and understanding of the life cycle of Leishmania are mandatory for all researchers who intend to dedicate their careers to the different aspects of this important disease. In order to support beginning researchers in the study of leishmaniasis, we propose in this review an update in the current knowledge about the major molecular aspects involved in the development of dimorphic forms of Leishmania parasites that replicate in the gut of sandflies (promastigotes) and in mammalian cells (amastigotes) and the relationship with host's immune system.

**Keywords:** neglected disease, protozoan, leishmania, amastigote, promastigote
