Prior to zygotic genome activation, early mammalian development relies on maternal-effect genes to orchestrate the oocyte-to-embryo transition. Recently, a subcortical maternal complex (SCMC) was identified to be essential for mouse preimplantation development. The SCMC integrates multiple proteins encoded by maternal-effect genes and appears to be functionally conserved across mammalian species. In addition, mutations in human SCMC genes are associated with certain human reproductive disorders. Here, we highlight recent advances in the biology of the SCMC and propose that this complex may be a representative example of maternal functional modules in mammalian oocyte-to-embryo transition. These findings may provide further insights into the molecular regulation of mammalian early embryogenesis, with possible implications for human early embryonic development and reproduction medicine.