A UK-based reseller's case against Microsoft regarding the resale of second-hand Windows and Office licenses is being heard by the UK’s Competition Appeal Tribunal (CAT) over three days, concluding on September 11. The court will determine if certain components of Microsoft's software are exempt from the EU’s software resale regulations, which currently allow the resale of perpetual software licenses. Microsoft argues that the resale doctrine applies only to computer programs and not to components like the graphical user interface (GUI), which they claim remain under copyright protection after license transfer. A ruling in favor of Microsoft could end the resale of second-hand Windows licenses in the UK. This case is part of a larger legal battle initiated by ValueLicensing in 2021, which accuses Microsoft of harming the pre-owned software market. The comprehensive trial is expected in 2026, but current proceedings may influence the case's direction. Additionally, with Windows 10 support ending soon, any increase in licensing costs could negatively impact users needing to upgrade their systems.