The embryophytes (land plants) have long been thought to be related to the green algal group Charophyta, though the nature of this relationship and the origin of the land plants have remained unresolved. A four-gene phylogenetic analysis was conducted to investigate these relationships. This analysis supports the hypothesis that the land plants are placed phylogenetically within the Charophyta, identifies the Charales (stoneworts) as the closest living relatives of plants, and shows the Coleochaetales as sister to this Charales/land plant assemblage. The results also support the unicellular flagellate Mesostigma as the earliest branch of the charophyte lineage. These findings provide insight into the nature of the ancestor of plants, and have broad implications for understanding the transition from aquatic green algae to terrestrial plants.