The health sciences largely focus on disease. However, the interconnected determinants of diseases suggest that we need a science of health, a framework to examine the biology of homeodynamics in a changing environment and how this affects the health we value. We build on first principles and recent discoveries on biological system dynamics to develop the concept of intrinsic health, a field-like state emerging from the dynamic interplay of energy, communication, and structure within the organism, giving rise to robustness/resilience, plasticity, performance, and sustainability. Intrinsic health is a quantifiable property of individuals that declines with age and interacts with context. We propose a measurement framework and describe how it will contribute to achieving the shared goals of medicine and public health.