The chapter discusses the importance of telomeres in protecting linear chromosomes from genome instability. Telomeres, composed of repetitive DNA sequences, form a protective nucleoprotein cap that shields chromosome ends from the DNA damage response (DDR). When telomeres are exposed, they can lead to genome instability and cancer. The chapter highlights the role of telomeric proteins, such as Shelterin, in maintaining telomere structure and function. These proteins help prevent chromosome fusion, regulate telomere length, and protect against DDR pathways. The chapter also explores the molecular basis of telomere dysfunction, including the loss of telomeric sequences, the failure of telomere capping, and issues with telomere replication. It discusses how dysfunctional telomeres can lead to genome instability and cancer, and the potential therapeutic targets for cancer treatment. Additionally, the chapter reviews the connection between telomere dysfunction and diseases such as Dyskeratosis Congenita (DC) and Idiopathic Pulmonary Fibrosis (IPF). Finally, it concludes by emphasizing the ongoing research into telomere biology and its implications for aging and disease.The chapter discusses the importance of telomeres in protecting linear chromosomes from genome instability. Telomeres, composed of repetitive DNA sequences, form a protective nucleoprotein cap that shields chromosome ends from the DNA damage response (DDR). When telomeres are exposed, they can lead to genome instability and cancer. The chapter highlights the role of telomeric proteins, such as Shelterin, in maintaining telomere structure and function. These proteins help prevent chromosome fusion, regulate telomere length, and protect against DDR pathways. The chapter also explores the molecular basis of telomere dysfunction, including the loss of telomeric sequences, the failure of telomere capping, and issues with telomere replication. It discusses how dysfunctional telomeres can lead to genome instability and cancer, and the potential therapeutic targets for cancer treatment. Additionally, the chapter reviews the connection between telomere dysfunction and diseases such as Dyskeratosis Congenita (DC) and Idiopathic Pulmonary Fibrosis (IPF). Finally, it concludes by emphasizing the ongoing research into telomere biology and its implications for aging and disease.