Transposable elements (TEs) are DNA sequences that can move from one location in the genome to another. TEs make up a large portion of the eukaryote genome throughout evolution, TE expression has been co-opted for nonpathogenic purposes. In the realm of development, these elements have been shown to play significant roles in the growth and differentiation of stem cells. TEs and their derived proteins have also been shown to play a significant role in the formation and function of the placenta. Following cellular differentiation and successful embryo implantation, TEs are also crucial in the development of the nervous system. Some evidence suggests that long noncoding RNAs produced from TEs may contribute to epigenetic networks crucial in neuronal differentiation. TEs are mainly expressed early in development and are gradually silenced by a myriad of mechanisms, including pre-transcriptional repression by DNA and histone methylation, and post-transcriptional repression by noncoding RNAs. In this chapter, we illustrate some of the known contributions of TEs to mammalian developmental programming, with an emphasis on examples in humans.