The article reviews the manifestations, genetics, and molecular mechanisms of telomere syndromes, which are a group of diverse disorders characterized by short telomere length. Telomeres are essential for maintaining genomic integrity and protecting chromosome ends from degradation and fusion. The progressive shortening of telomeres with cell division and aging has led to the concept of a 'molecular clock' that may contribute to age-related diseases. Telomerase, an enzyme that adds telomeric DNA, is upregulated in many cancers and has been pursued as a target for cancer treatment. Recent genetic discoveries have linked specific telomere genes to monogenic disorders, such as dyskeratosis congenita, Hoyeraal–Hreidarsson syndrome, and Revesz syndrome. These disorders share a common underlying defect of short telomere length and can manifest as childhood or adult-onset diseases. The clinical spectrum of telomere syndromes includes bone marrow failure, pulmonary fibrosis, and cancer, with a particular predisposition to cancer in patients with these syndromes. Telomere length is a heritable trait and a modifier of disease severity and type, influencing the onset and progression of diseases. The review highlights the importance of understanding telomere biology in the context of age-related diseases and the potential for novel therapeutic approaches.The article reviews the manifestations, genetics, and molecular mechanisms of telomere syndromes, which are a group of diverse disorders characterized by short telomere length. Telomeres are essential for maintaining genomic integrity and protecting chromosome ends from degradation and fusion. The progressive shortening of telomeres with cell division and aging has led to the concept of a 'molecular clock' that may contribute to age-related diseases. Telomerase, an enzyme that adds telomeric DNA, is upregulated in many cancers and has been pursued as a target for cancer treatment. Recent genetic discoveries have linked specific telomere genes to monogenic disorders, such as dyskeratosis congenita, Hoyeraal–Hreidarsson syndrome, and Revesz syndrome. These disorders share a common underlying defect of short telomere length and can manifest as childhood or adult-onset diseases. The clinical spectrum of telomere syndromes includes bone marrow failure, pulmonary fibrosis, and cancer, with a particular predisposition to cancer in patients with these syndromes. Telomere length is a heritable trait and a modifier of disease severity and type, influencing the onset and progression of diseases. The review highlights the importance of understanding telomere biology in the context of age-related diseases and the potential for novel therapeutic approaches.