Hydrogen atoms can provide high phonon frequencies and strong electron-phonon coupling in hydrogen-rich materials,which are believed to be potential high-temperature superconductors at lower pressure than metallic hydrogen.Especially,recently both of theoretical and experimental reports on sulfur hydrides under pressure exhibiting superconductivity at temperatures as high as 200 K have further stimulated an intense search for room-temperature superconductors in hydrides.Tbis review focuses on crystal structures,stabilities,pressure-induced transformations,metallization,and superconductivity of hydrogen-rich materials at high pressures.