Aneuploidy is an abnormal number of chromosomes, and is a type of chromosome abnormality. An extra or missing chromosome is a common cause of genetic disorders. Some cancer cells also have abnormal numbers of chromosomes. Aneuploidy occurs during cell division when the chromosomes do not separate properly between the two cells. Chromosome abnormalities occur in 1 of 160 live births. In this book, the authors present topical research in the study of the etiology, disorders and risk factors of aneuploidy, including the role of environmental pollutants as a mechanism of aneuploidy; ploidy in mitosis and meiosis; the spindle assembly checkpoint and aneuploidy; cohesions, genomic stability and cancer and aneuploidy in cultured human multipotent mesenchymal stromal cells.