Summary Our cells are constantly exposed to mutagens that cause DNA damage, which if left unrepaired, cause mutations. At the cellular level, the progressive accumulation of mutations in somatic tissues drives carcinogenesis and other diseases. Despite significant advances in our understanding of mutational processes, the answer to many fundamental questions is still a mystery. What are the genetic causes of mutations in human tissues? How do different cell types in the human body control DNA damage and repair? Despite our large body of knowledge in the pathways that control DNA damage and repair in model organisms, we lack a deep understanding of this process in human tissues. This would be critical to understand how mutations lead to human diseases including carcinogenesis. Here we will use a highly innovative approach to build MutSensor, a set of mutation reporters to estimate DNA mutation frequency in mammalian cells with a sensitivity >50-fold higher than that of existing methods. The ability to build and precision deliver these MutSensors is enabled by “Genetic Writing and Delivery” system developed in the Boeke lab. This novel method will allow large-scale functional genetic screening at an unprecedented scale. Building on our preliminary data, we aim at comprehensively identify all genes that regulate mutation frequency in different human cell types. To this purpose, we will utilize loss- and gain-of-function screening libraries to determine the effect of genetic perturbations on mutation frequency across cell types. These studies will provide an unprecedented systematic map of genes and pathways controlling DNA damage and mutations across different human cell types. In addition, our novel methodology will represent an important asset for the scientific community that can have several biomedical applications in a variety of fields providing an easy tool to study genetic factors that control mutagenesis in health and disease states, including (but not limited to) carcinogenesis.