Telomeres, the natural ends of linear eukaryotic chromosomes, are specialized protein-DNA complexes that play essential roles in cell viability and genome integrity. The long-term goal of my research is to understand how telomeres protect chromosome ends and mediate their replication by telomerase. A six-protein complex, called shelterin, associates with telomeres and protects the ends of human chromosomes. A major gap in our knowledge of the shelterin complex is how its protein components organize at telomeres. I will present our recent studies that reveal the molecular architecture and functional significance of the shelterin complex.