Preimplantation embryos generate intercellular junctions during differentiation of the trophectoderm epithelium and the formation of the blastocyst. These membrane complexes comprise gap junctions, adherens junctions, tight junctions, and desmosomes, each performing fundamental roles in cellular communication, adhesion, and differentiation. The mouse embryo has been used as a model for the biogenesis of cell junctions. Their construction is achieved by temporally regulated gene expression programs. Mechanisms of junction membrane assembly include the timing of transcription, translation, and post-translational modifications of specific junctional proteins. Human embryos exhibit similar expression programs, and defects in these programs may contribute to reduced embryo viability.