Adapting California’s water management systems in response to climate change presents one of the most significant challenges for the 21st century. In the course of the past five years, the California Department of Water Resources has taken an active role in both identifying opportunities to mitigate greenhouse gas (GHG) emissions and in positioning California to adapt to changes happening now and in the future. The recent publication of the Climate Change Handbook for Regional Water Planning is the most recent effort to bring together two separate water planning efforts – integrated regional water management and climate change mitigation and adaptation. The key to this planning synthesis is a significant change in the way water planners have addressed issues of water management. This paper looks at the development of integrated regional water management and climate change planning by the CDWR and their current union in the Handbook.