Defect healing of the uterotomy at ceasarean section (CS) results in a morphological und probably functional disruption of the anterior uterine wall. Clinical sequelae concern subsequent pregnancies with a broad range of complications before and during pregnancy as well as at birth. In the following chapter, we provide an overview about the definition, diagnosis, symptoms and pathogenetical mechanisms of CS scar defects. Keeping in mind the pathogenesis allows to introduce preventative approaches.