Telomeres and their associated proteins are specialized structures at the ends of linear chromosomes that function as caps that protect the DNA from exonuclease degradation and recombination events that could lead to genomic instability. In this review, we discuss recent publications describing the high-resolution structures of individual domains and of the full-length catalytic subunit of telomerase alone and in complex with its putative RNA template and telomeric DNA. These structures, together with existing biochemical data, provide novel insights into the basic mechanism of telomere replication and length homeostasis by telomerase. Moreover, these data further enrich our understanding of the mechanism of DNA replication by polymerases in general and they provide a framework to design small molecule inhibitors of telomerase that may be of therapeutic value for cancer and other diseases associated with cellular aging.