||The past decade has seen tremendous advances in technologies for achieving extreme conditions such as static high pressure, shock wave, high/low temperature, high magnetic field, irradiations, as well as large strains and quantum confined systems. These advances are opening a new era in materials discovery with orders of magnitude more materials to be produced at extremes than all that have been explored at ambient condition. Under extremes, materials will exhibit emergent and/or enhanced properties and functionalities that cannot be obtained using traditional methods. Challenges exist, however, in realizing these extreme systems and in developing associated characterization methodology under extremes. In-situ and operando techniques implemented at accelerator-based large-scale facilities (synchrotron, neutron and free-electron-laser sources) are highly desirable to investigate the structural and property changes of materials under extremes, as well as to develop decisive understanding of the structure-property relationship and underlying mechanisms for the emergent properties. With the development of advanced characterization methods, together with novel extreme technologies, numerous exciting opportunities are emerging for materials research at extremes. We envision this symposium to highlight most recent findings, trends, and perspectives in new materials and novel phenomena at extreme conditions and the associated cutting-edge characterization technologies.