In multicellular life, a single cell gives rise to different organs, tissues and cell types. Cells rely on many signals to determine their role, such as the highly conserved WNT/beta-catenin (WNT/CTNNB1) pathway. As disruption of this pathway is implicate in many cancers and diseases, improved understanding could improve current treatments. The molecular mechanisms of WNT/CTNNB1 signaling were discovered through genetic and biochemical analyses. However, we currently lack information on its spatiotemporal dynamics. In this thesis, we first use CRISPR/Cas9-mediated genome editing to quantify the dynamics of fluorescently tagged CTNNB1 at endogenous levels in HAP1 cells. With this data we generate a computational model that shows CTNNB1 is regulated at three distinct levels: its degradation, its nuclear/cytoplasmic shuttling and its binding to nuclear partners. We then characterize a mouse model which also expresses fluorescent CTNNB1 at endogenous levels and show its use as a marker for WNT/CTNNB1 signaling. Importantly, the small changes we measure in CTNNB1 across a large range of biological settings, is consistent with our work in human cells, which highlights the tight regulation of CTNNB1 levels and localization and the importance of small spatiotemporal changes in signaling. To further investigate how CTNNB1 is regulated, we perform insertional mutagenesis screens in dual reporter cells. In this way we identified regulators that act on CTNNB1 levels or transcriptional activity and follow up on a new transcriptional regulator: SETD1B. Finally, we discuss the challenge in visualizing and measuring small changes, and the relevance of these changes in signal transduction.