Mammalian ovarian development involves unique interactions between the germ-line and somatic genomes. Several regulators affect gene expression, including a class of small RNAs called microRNAs (miRNAs). miRNAs are small, noncoding, regulatory RNAs that are 19 to 25 nucleotides long. miRNAs regulate gene expression in part via translational control of messenger RNAs (mRNAs). miRNAs are expressed during different stages of mammalian ovarian development and are likely to play important roles during gonadal development and folliculogenesis. The role of individual miRNAs in mammalian ovarian development is currently unknown and will remain an important focus for future investigations.