Leishmania tarentolae is a trypanosomatid protozoan parasite of the gecko, and has been established as a new eukaryotic expression system for the production of recombinant proteins. It seems that a protozoan parasite is a curious choice as the expression host; however, Trypanosomatidae are rich in glycoproteins with a pattern of glycosylation closely related to those in mammals and higher vertebrates. Thus, one of the main advantages of a L. tarentolae expression system is the mammalian-type posttranslational modification of target proteins. Although there are few examples of recombinant protein expression using this system, it can be an attractive alternative to using mammalian cells. This chapter presents an overview of the newly developed protein expression system based on L. tarentolae.