Healthy environments inspire and support healthy populations, yet the environment is being altered at an unprecedented rate and magnitude. California is at the epicenter of droughts and unsustainable resource consumption. In the most vulnerable regions globally, rapid population growth and urbanization collide with climate change. Achievable responses to large scale health and environment transitions will be intrinsically integrative, multidisciplinary, multi- campus, and will involve stakeholders globally and locally. The Center of Expertise on Planetary Health envisions a healthy planet supporting healthy people. Towards this vision, the mission of the Center is to lead the world in science, education, outreach, and transformative solutions to coupled health- environment challenges. The Center will galvanize faculty, researchers, and students at the ten UC campuses who share a common vision of the threats and opportunities surrounding the health of populations and their environments at this urgent historical crossroad.