Measuring the SM scalar CP-properties using the H→𝜏𝜏 decay channel The standard model (SM) Brout-Englert-Higgs (BEH) sector predicts exactly one physical scalar boson H with CP-even couplings to the SM particle. However, many extended SM scalar sectors such as two BEH doublet models contain additional CP-phases which can lead to detectable CP-violating interactions between the SM scalar boson and the SM particles. Evidence of such interactions would therefore conflict with the SM predictions and directly indicate the presence of a non-minimal BEH sector. These additional CP-phases could also provide insight into the observed excess of matter over antimatter in the universe. Several analyses by the CMS and ATLAS collaborations to date have measured the CP properties of the observed 125 GeV boson and found no evidence for CP-odd contributions. However, most of these measurements have utilised interactions involving BEH coupling to the weak gauge bosons, where CP-violating effects are typically suppressed due to a lack of corresponding tree-level CP-odd couplings. On the other hand, CP-odd BEH couplings to fermions can occur at tree level and therefore interactions involving such couplings are ideal for studying the CP properties of the SM scalar boson. This seminar will discuss the first direct measurement of the CP properties of the BEH to tau tau coupling by the CMS experiment, using the 13 TeV dataset collected during the 2016-2018 data taking period. Prospects for improving such measurements using data collected in future LHC runs and by proposed electron-electron colliders are also reviewed.