Derive T 6 for the Windows T operating system is the most recent evolution of the Derive user interface. This presentation will review the progression from Derive 4 in light of the following challenges: adherence to user interface design guidelines; addition of new features while maintaining simplicity; trade-offs in meeting user requests; and simultaneous software releases in multiple languages. With an updated systems architecture diagram as a baseline, we will explore the major interface components and process flow of several Derive features. Topics such as expression entry, plotting, interconnectivity with TI CAS calculators, and "Display Step" will be illustrated.