Reflecting the severity of global food insecurity, over 60% of the East African population is considered malnourished, with many regions in a state of famine. There is broad agreement on the need to help small-scale farmers move from subsistence to sustainable and profitable farming by boosting their agricultural productivity, reducing post-harvest spoilage losses and providing market linkages. Most countries in East Africa have an agrarian economy with over 80% of the households depending on agriculture for their livelihoods. The climate is characterized by biannual dry seasons where many farmers suffer due to water shortages and poor soil nutrition. While short periods of rain benefit local farmers, heavy rainfall sometimes destroys cash crops. Greenhouses are permanent glass or plastic-covered structures that allow farmers to grow vegetables and fruits year-round through mechanically-controlled temperature and irrigation systems. Greenhouses can help farmers in East Africa grow and protect crops in both wet and dry seasons. Large commercial farms employ large greenhouses to produce high-value cash crops for the export market. East African companies import and sell greenhouses priced at over US 2,000 to commercial farmers. While greenhouses can significantly increase smallholder productivity and improve livelihoods, current designs are inappropriate and too expensive. The adoption of affordable and context-appropriate greenhouses can lead to improved livelihoods for farmers and entrepreneurs while fostering food security. This paper describes the constraints and design tenets for low-cost (~200 bill of materials) greenhouses and discusses results from three years of field-testing such greenhouses in Kenya, Tanzania and the United States. Currently, the field-tested prototypes excel in affordability, maintenance, and crop protection. This paper seeks collaborators to refine and localize the technology with the ultimate objective of disseminating it broadly.