The 21st century will be defined by challenges such as understanding and preparing for climate change and ensuring the availability of resources such as water and energy, which are issues deeply rooted in Earth science. Understanding Earth science concepts is critical for humanity to successfully respond to these challenges and thrive in the decades to come. As part of efforts to address this, a new program called the Earth Science Literacy Initiative (ESLI) was formed in 2008 with funding from the National Science Foundation (NSF). Its task was to create a succinct document outlining what citizens should know about Earth science. This document, called the Earth Science Literacy Principles (ESLPs), has applications in both public and private arenas. For example, the ESLPs have been used to define the core ideas of both a middle school textbook program and a new set of K-12 science education standards. The ESLPs, which are founded in a broad representation of the geoscience community, based upon current research, and endorsed by major government, industry, and academic geoscience organizations, represent an effort by the Earth science community to create a coherent and fundamental set of big ideas and supporting concepts that represent our fields.