Down syndrome (DS) is a chromosomal disorder caused by an extra copy of most or all of human chromosome 21 (Hsa21), which contains over 200 protein-coding genes and more than 400 non-protein-coding genes. This trisomy results in the overexpression of most of these genes, presenting a challenge in identifying those responsible for specific symptoms of DS. Moreover, some DS symptoms may result from interactions among multiple genes. Drosophila melanogaster, with its short lifecycle and capacity for easy genetic manipulation, is a valuable model for such research. Approximately half of the protein-coding genes on Hsa21 have Drosophila homologs, enabling the study of these genes in a simpler genetic model. This chapter outlines key Drosophila techniques used to explore DS mechanisms, reviews significant research contributions, and discusses the limitations of using Drosophila models to understand DS pathogenesis.