Foliar fertilization (or foliar feeding) entails the application—via spraying—of nutrients to plant leaves and stems and their absorption at those sites. Used in both conventional and alternative production systems, it is a viable (though somewhat controversial) means of enhancing crop nutrition. Because information on conventional applications of foliar feeding is usually available through Cooperative Extension and the general farm press, this publication will stress applications in sustainable and organic agricultural systems. For more detail on what is meant by “sustainable” and “organic” agriculture, request ATTRA’s Sustainable Agriculture: An Introduction and Overview of Organic Crop Production.