The preservation of expected life span and longevity, as well as the assurance of life succession among all species requires the integrity and faithful transcription of DNA. A dedicated machinery of DNA repair factors is responsible for reversing DNA damage across the genome. Efficient response to various effectors of DNA damage is also dependent on a complex network of sensors and mediators of stress signals which are upstream of DNA repair activation and together constitute components of the DNA damage response (DDR). This book reviews research on cell cycle checkpoints as essential mechanisms for safeguarding genome stability; nucleotide excision repair (NER) which recognises and removes bulky DNA damage that leads to DNA double-helix distortion and others.