The next frontier.

High-intensity lasers are opening up a new realm of light-matter interactions. In his Perspective, Yamanouchi reviews recent progress in this field, focusing on two intensity regimes: the Coulombic regime, which mostly deforms molecular structures and causes tunneling ionization, and the relativistic regime, where high-intensity lasers produce x-rays and high-energy particles and may cause nuclear fusion reactions. Efforts are under way to increase laser intensity further for accessing the next frontier.