MicroRNAs (miRNAs), small noncoding RNAs that post-transcriptionally regulate gene expression, are one of the most abundant classes of gene regulators. Yet, little is known about the roles that specific miRNAs play in the development of multicellular organisms. Drosophila provides an excellent model system to explore the in vivo activities of particular miRNAs within the context of well-defined gene-expression programs that control the development of a complex organism. This chapter reviews the various approaches currently used to identify Drosophila miRNAs, detect their expression, determine their messenger RNA targets, and study their function.