Throughout their lifetime, animals face a wide variety of biological challenges. Starting out as single cells, their _rst challenge is to undergo development and become fully grown and functional adults. Remarkably, this incredibly complex process occurs in a highly reproducible manner despite the huge variability in environmental, genetic and molecular uctuations they encounter during their journey through development. However, the challenges do not end here; once animals become adults, their tissues are constantly subject to damage, either by external sources such as disease, or due to intrinsic causes such as cellular aging. Thus, adult tissues are constantly renewing themselves, and must do so in a tightly controlled manner in order to maintain homeostasis. In this thesis, we explore how animals cope with a few of such challenges with the help of two model systems, C. elegans worms and stem cell-derived organoids. @en