This document presents 13 priority science actions that fill critical gaps in Delta science, gluing disparate pieces of this complex enterprise together to advance the vision of the Delta Science Plan: One Delta, One Science. The document organizes and summarizes these priorities under five thematic science action areas. These action areas and priorities were identified through an open and transparent process that gathered input from the Delta Science community, the public, and major synthesis efforts; examined peer-reviewed literature; and involved review by the Delta Independent Science Board. The document details each action area and discusses how the agenda can be used to promote collaborative science, improve efficiencies in science planning, and coordinate investments in critical science investigations and infrastructure. Request access to the Science Action Agenda by contacting firstname.lastname@example.org.