Chromosome end protection is essential for all organisms with linear genomes. Specialized structures, called telomeres, accomplish this protection by forming DNA-protein complexes that hide the natural chromosome ends from the DNA damage machinery. In mammalian cells protection takes place on several levels. Telomeric DNA forms large duplex loops with the help of telomeric proteins, consequently hiding the very tip of the telomere. Telomeric proteins play additional roles in protecting the end from degradation, regulating telomere length, and suppressing the DNA damage response machinery. Here we summarize the current knowledge about telomere structure, and discuss the future directions of the field.