It's likely that as long as humans have made note of plant function, the legume family has been of interest. Not only do legumes provide fodder for animals and nutrition-rich seeds for humans, but ancient cultures were aware of the ability of many legumes to improve the soil, a result of symbiotic nitrogen fixation, as we now know. As Mendel's study organism, the legume pea (Pisum sativum) became the first model system for quantitative genetics. And through the 20^th century, crop legumes were the topic of innumerable physiological studies on environmental responses, biotic interactions, metabolism, and development.

Recently, the pace of discovery in legume biology has accelerated, fueled by the development of two model systems for modern molecular genetic analysis and by the application of genomic approaches. These advances culminated last year with the first successful positional cloning of legume genes from Medicago spp., Lotus japonicus, and soybean (Glycine max). We expect the current momentum to be sustained, as more investigators make use of genetic and genomic tools for in depth studies of key species and for comparative analysis with other crop legumes. This trend is supported by the recent National Research Council assessment of goals for the future of the National Plant Genome Initiative (for the review committee's full report, see http://books.nap.edu/books/0309085292/html/index.html; also see The National Plant Genomics Initiative: Objectives for 2003-2008. Plant Physiol 130: 1741-1744). The committee's recommendations included expanded emphasis on genomic sequencing of reference species including Medicago truncatula, draft sequencing of the gene-rich regions of selected crops including soybean, and application of genomic resources to dissect evolutionary radiation of adaptive traits in related species.

In June 2002, the first International Conference on Legume Genomics and Genetics (ICLGG) in Minneapolis gave a taste of this integrative approach (program and abstracts are available at http://www.agro.agri.umn.edu/iclgg/). The conference brought together about 300 researchers who work on L. japonicus and Medicago spp., soybean, bean (Phaseolus vulgaris), pea, and many other species. Systematists rubbed shoulders with developmental and molecular biologists, and breeders tapped the accumulated expertise in genomics and bioinformatics. The gathering provided the kind of intellectual ferment that fosters multinational and interdisciplinary collaborations. Plans are already under way for the second ICLGG, which will be held in Dijon, France, in conjunction with the European Association for Grain Legume Research meeting in June 2004.

This issue of Plant Physiology focuses on the biology of legumes. It highlights the development of research tools and their application to problems in legume biology. This issue also provides updates on the diversity of legumes and aspects of plant function of special significance in the Leguminosae, including symbiotic interactions, nutritive qualities of seeds, and natural products. Therefore, we hope that readers will find here not just a retrospective of work on this important plant family, but also a guide to future targets in research.