During the past decades, cancer research has expanded rapidly due to the relatively high incidence rate of cancer and high death rate linked to it. The type and the extent of aggressiveness of particular cancers are determined by specific flaws in the cell cycle regulation. Cancer is the clonal collection of cells which possess high aggressive behaviour and therefore it is considered to be a proliferative disease. Such behaviour is due to genetic instability which is defined as an increase in the rate of genomic mutations caused by defects in the genes which are responsible for the checkpoints in the cell cycle. In this book, various issues were discussed including: pre-invasive central diseases and cervical carcinoma, genetic screening of heredity diseases, inherited cancer syndromes, tumor suppressor genes, acute and chronic leukaemia as well as the role of cell cycle regulation in cancer.