Each year, 5 million people die of malnutrition, 3.5 million of whom are children under the age of 5. To meet the global challenge of producing enough food, we need inexpensive and sustainable approaches to improving productivity -- not only of the major commodity crops, but also local crops of all kinds. Taking advantage of the unique properties of microbes is one of the most promising ways to achieve this. All plants evolved in a world dominated by viruses, bacteria, and fungi; over millions of years, plants and microbes have formed many mutually beneficial relationships. Microbe-plant partnerships improve plant resistance to many stresses, including disease, drought, salinity, limited nutrients, and extreme temperature. Recently, there have been significant advances in understanding the natural relationships between plants and microbial communities and how they can be used to increase the productivity of almost any crop, anywhere, potentially at a reasonable cost and without corollary harm to the environment. Together, such approaches could spark a new microbially driven Green Revolution. Based on a colloquium convened in November 2012 by the American Academy of Microbiology, speakers in this session will describe ways that the long-evolved relationships among plants and their many microbial partners can be used to significantly improve global crop productivity, grow crops on marginal soils, minimize post-harvest loss, and protect crops from pests and pathogens.