MicroRNA (miRNA) are small RNA molecules of about 20–25 nucleotides in length which act to regulate gene expression post-transcription primarily by blocking the translation of messenger ribonucleic acid (mRNA). miRNA play important roles in the pathology of cancer, and also during normal pregnancy and lactation. The study of miRNAs related to cancer screening and treatment is perhaps the most developed of the clinical applications regarding miRNA, particularly for breast cancer. Evidence miRNAs affect pregnancy is strong, but the specifics remain poorly understood as the relationship between mother and neonate is complex. Within this relationship, miRNA in milk remain the most unknown, but it is hypothesized that milk miRNA play a role in regulation of both the mammary gland and in the neonate. This chapter describes ways biomedical researchers would gain from viewing miRNAs from an evolutionary perspective, specifically for research involving potential therapeutic interventions for women.