The discovery of the postperovskite (PPv) transition has profound impact on our understanding of the core-mantle boundary (CMB) region. Unlike perovskite (Pv), the PPv phase has a layered structure of the SiO6 octahedra, which may lead to a large contrast in some properties with Pv. Recent studies have proposed unusual properties of PPv, such as a large positive Clapeyron slope, a large sensitivity of the transition depth to iron, a decrease in bulk sound speed at the transition, and a development of significant lattice preferred orientation. Many of the proposed properties can provide explanations for the intriguing seismic observations at the CMB region. Yet significant discrepancies still exist. However, rapid developments in mineral physics will continue to improve our knowledge on the changes across the PPv transition. mantle, core-mantle boundary, mantle dynamics, mantle structure, D″ region.