With the continuous development of high power laser technologies, lasers with peak power at 10 petawatt (PW) or above are becoming available soon in a few laboratories worldwide. Such lasers may be focused to an intensity above 10²³ W/cm², at which heavy elements such as uranium can be stripped of electrons, entirely leaving behind pure atomic nuclei, and electrons can be accelerated to more than 10 GeV. We are entering an unprecedented regime of laser-matter interactions, where collective effects, relativistic effects, and quantum electrodynamic (QED) effects all play significant roles. Extremely rich nonlinear physics in this regime could be tested experimentally, such as radiation reaction, gamma-ray and pair production via different processes, laser driven nuclear physics, laser-vacuum polarization, etc. It is expected that the new understanding of physics for these extreme high field conditions will lead to a wide range of applications.