The New Zealand Earth System Model (NZESM) is currently under development to help inform scientists, policy makers, climate-sensitive sectors of the economy, and the general public in New Zealand about climate change. The term `climate model' is generally used to describe a computer model that incorporates physical aspects of the climate system such as atmospheric and oceanic fluid mechanics and thermodynam- ics. In addition, Earth System Models represent aspects of biology and chemistry such as marine biogeochemistry and atmospheric ozone chemistry. The development of the NZESM represents a step-change in model complexity for New Zealand science, and a major motivation for its development is to reduce Southern Hemisphere specific mod- elling problems such as the formation of Southern Ocean sea ice and Antarctic Bottom Water. The atmosphere, land surface, ocean and sea ice components of the model are already available in New Zealand. In the future, additional models representing (for ex-ample) ocean biogeochemistry and marine ice-sheets will also be added to the NZESM framework. Over the next 5 years, the NZESM will be run to produce hindcasts for the past 150 years and projections for up to 200 years into the future. Such experiments will "... enable New Zealanders to adapt, manage risk, and thrive in a changing climate", which is the mission statement of the Deep South National Science Challenge. Over the next decade, the NZESM will be used in Earth System science research throughout New Zealand, both in terms of pure science and via communication of its results to New Zealanders.