This chapter examines the philosophical and practical challenges of health measurement, a crucial tool for understanding treatment impacts, addressing inequalities, and guiding policy. Despite its importance, health measurement often operates as a “black box,” with constructs and validity remaining unclear. Instruments like the SF-36 and EQ-5D, widely used for health-related quality of life (HRQoL), reflect diverse approaches, yet their conceptual underpinnings often go unexamined. Measures are not neutral; they embody ethical and political assumptions that shape how health is defined and assessed, especially when used as tools to allocate healthcare resources. Structural injustices further complicate measurement, with marginalized groups facing significant data quality issues.