Plants exploit several types of cell surface receptors for perception of extracellular signals,of which the extracellular leucine-rich repeat(eLRR)-containing receptors form the major class.Although the function of most plant eLRR receptors remains unclear,an increasing number of these receptors are shown to play roles in innate immunity and a wide variety of developmental processes.Recent efforts using domain swaps,gene shuffing analyses,site-directed mutagenesis,interaction studies,and crystallographic analyses resulted in the current knowledge on ligand binding and the mechanism of activation of plant eLRR receptors.This review provides an overview of eLRR receptor research,specifcally summarizing the recent understanding of interactions among plant eLRR receptors,their co-receptors and corresponding ligands.The functions of distinct eLRR receptor domains,and their role in structure,ligand perception and multimeric complex formation are discussed. Plants exploit several types of cell surface receptors for perception of extracellular signals, of which the extracellular leucine-rich repeat (eLRR) -containing receptors form the major class. Although the function of most plants eLRR receptors remains unclear, an increasing number of these receptors are shown to play roles in innate immunity and a wide variety of developmental processes. Recent efforts using domain swaps, gene shuffing analyzes, site-directed mutagenesis, interaction studies, and crystallographic analyzes resulted in the current knowledge on ligand binding and the mechanism of activation of plant eLRR receptors. This review provides an overview of eLRR receptor research, specifcally summarizing the recent understanding of interactions among plant eLRR receptors, their co-receptors and corresponding ligands. The functions of distinct eLRR receptor domains, and their role in structure, ligand perception and multimeric complex formation are discussed.