The Fundamental User Needs (FUN) Scales is a newly introduced instrument tailored to assess how design-mediated interactions influence users' need satisfaction and frustration. The FUN Scales offer significant value to HCI and design research and practice, including the following benefits: Provides a shared and consistent language for discussing user needs, enabling standardized evaluations and comparisons across different projects and studies. Facilitates collaboration between HCI experts, designers, engineers, and other stakeholders by offering a common framework for understanding user needs. Bridges the gap between theoretical research on basic psychological needs and practical HCI and design applications, ensuring design decisions are evidence-based. Supports the development of need-oriented design principles, grounded in empirical research, that prioritize fundamental user needs in design-mediated interactions. Empowers informed design decisions, guiding the design of features and functionalities that focus on fulfilling fundamental users' needs.