This chapter reviews biological processes that are related to health and disease. In particular, biological processes including processes that transmit information about the external environment to the rest of the body via neural and neuroendocrine signaling, and biological processes (immune, metabolic, and cardiovascular) that are directly involved in disease pathophysiology, are discussed. The chapter also covers issues related to conceptualization and measurement of biomarkers and when such biomarkers can be considered health outcomes. Conceptual issues include the different functions of biological processes (promoting adaptation during environmental challenges or restoring function), the cellular and molecular mechanisms that ultimately link the external environment with changes in the body, in addition to gene and environmental contributions to individual differences. Implications for research across the translational spectrum, the lifespan, and for understanding socioeconomic- and ethnicity-related health disparities are also reviewed.