The Hippo pathway is required for normal tissue growth during development and it is also involved in regeneration in flies and mammals. Hyperactivation of the Hippo pathway effector YAP drives cell proliferation and malignancy of tumor cells and YAP is frequently hyperactivated in a broad range of different human carcinomas. Thus, targeting the activity of YAP may inhibit cancer cells. However, how the Hippo pathway is regulated during development and what role it plays during normal growth, regeneration, and in cancer cells is poorly understood. My group uses genetic approaches in Drosophila and mice to unravel the function of the Hippo pathway and to dissect its regulation during organ growth control and regeneration. I will present our recent efforts towards these aims and discuss our findings in light of different growth control models.