Medicago truncatula is a major model legume developed to study symbiotic associations such as legume nodulation and arbuscular mycorrhizae and also a wide variety of biological topics from plant development and pathology to evolution and ecology. We have recently utilized new tandem mass spectrometry technology to map 3,404 non-redundant sites of phosphorylation on proteins from Medicago roots (Grimsrud et al. 2010). Analysis of this data has revealed novel plant protein phosphorylation motifs and previously unreported phosphorylation sites on proteins involved in symbiotic signaling as well as many proteins with central roles in plant biology. This online database was created to provide the research community with an easy way to access legume phosphoproteomic data generated from this and future studies. When citing The Medicago Phosphoprotein Database