The single molecule of DNA that constitutes a eukaryotic chromosome begins and ends with a stretch of repetitive DNA known as a telomere. These sequences appear to be necessary to preserve the integrity of the genetic material through the cell cycle.Telomeric DNA is organized into regions of non-nucleosomal chromatin called the telosome, which can interact with other telosomes and with the nuclear envelope. This review focuses on cytological evidence for these interactions and on recent insights into the molecular organization of the telomeric complex.