Bon Kyoung Koo is an experienced mouse geneticist actively employing the emerging organoid culture technology to study stem cell maintenance and activation in mouse and human intestinal and stomach organoid cultures. He is also an expert in genetic engineering. Following his PhD and first post-doctoral studies in the laboratory of Young-Yun Kong at POSTECH – Republic of Korea, Koo joined the group of Hans Clevers at the Hubrecht Institute, KNAW, Netherlands. Here he witnessed the first establishment of the Lgr5+ cell-derived intestinal organoid culture system pioneered by Toshiro Sato and Hans Clevers. In the following years Koo has utilised this novel culture system to perform sophisticated gene correction studies, to unravel the molecular regulation of adult stem cells and to proof the stem cell properties of a Troy+, quiescent reserve stem cell population in the stomach. His group has also developed novel genetic tools to further investigate how proliferating and quiescent adult epithelial stem cell populations are regulated both in homeostasis and during injury-mediated repair.