Leishmania parasites are etiological agents of a wide spectrum of diseases in humans, denominated leishmaniasis. Clinical forms of these diseases range from self-healing cutaneous lesions to disseminated, mucocutaneous, and fatal visceral infections affecting over 12 million people worldwide. Both parasite species and host immune responses contribute to the clinical outcome. During the last decades, impressive advances in sequencing the genome of most of the pathogenic Leishmania spp. has been accomplished resulting in remarkable improvements in the understanding of parasite biology. Despite these successes, the few differences identified at the genome level among Leishmania species do not explain the broad spectrum of clinical manifestations caused by these parasites. Because Leishmania regulates gene expression at the posttranscriptional and posttranslational levels, a poor correlation is observed between transcripts and protein levels. In such scenario, proteomics analysis represents an impair tool for understanding the contribution of parasites to clinical outcomes. However, the achievements in large-scale proteomics analyses did not follow the genomic efforts and the Leishmania proteome remains largely uncharacterized. Proteomics intends to provide detailed descriptions and integration of protein data to better ascertain protein function in biological systems. Proteomics studies in Leishmania spp. have focused on global proteome profiling, identification and quantification of proteins related to the different evolutionary forms, and proteins enriched in different cellular fractions or organelles. Also, relevant contributions have been made to the description of posttranslational modifications, quantification of the abundance of proteins in response to drugs, and those involved in the regulation of the host immune response. These qualitative and quantitative profiles have contributed to the functional annotation of proteins, the identification of molecules involved in virulence and drug resistance, in addition to expand the design of vaccines and therapeutic alternatives. Here, we present a historical review on the contribution of proteomics to the understanding of Leishmania biology.