The United States has the world’s largest marine Exclusive Economic Zone, an area of ocean along the nation’s coast lines which is equivalent to the total land area of all 50 states. The nation has the potential to utilize this resource to build and grow a thriving marine biomass industry for the production of fuels, chemicals, feed, and food. Growing macroalgal biomass in the oceans offers a unique opportunity to sidestep many of the challenges associated with terrestrial biomass production systems, particularly the growing competition for land and freshwater resources, which are likely to result from the 50 to 100% increase in demand for food expected for 2050. The overall goal of this program is to develop the critical tools that will allow the nascent macroalgae industry in the United States to leverage this tremendous resource and grow into a world leader in the production of marine biomass. The program will focus on developing advanced cultivation technologies that enable the cost and energy efficient production of macroalgal biomass in the ocean at a scale suitable as feedstock for the production of fuels and chemicals. The challenge is to dramatically reduce capital and operating cost of macroalgae cultivation, while significantly increasing the range of deployment by expanding into more exposed, off-shore environments. Specifically, this program is interested in new designs and approaches to macroalgae cultivation, with harvesting and transport being an integral part of such systems. These new systems may leverage new material and engineering solutions, and autonomous and robotic operations, as well as advanced sensing and monitoring capabilities. To further accelerate the development and deployment of such systems, the program will also focus on the development of computational modeling tools and ocean- deployable sensor platforms, as well as advanced macroalgal breeding tools. ARPA-E expects that the MARINER program will support development of technologies that will accelerate the deployment of advanced ocean farming systems capable of delivering renewable biomass feedstock at a cost competitive with terrestrial biomass feedstocks.