The diversity of groundwater governance (making laws, policies, and regulations) within the United States makes describing generalities difficult, as each state determines its own groundwater priorities and governance approaches. Sometimes states delegate significant reponsibilities to sub-state jurisdictions. This chapter in the book Advances in Groundwater Governance, written by Sharon B. Megdal, Adriana Zuniga Teran, Robert G. Varady, Nathaniel Delano, Andrea K. Gerlak and Ethan T. Vimont demonstrates the changing nature of groundwater governance and groundwater debates by considering California and Arizona. Arizona has a long history of practicing groundwater management in designated parts of the state, while California recently adopted a more comprehensive, state-wide approach.