This chapter highlights the importance of identifying health risk factors and their parameters for healthier built environments. In Sect. 3.1, epidemiological terms such as "determinants of health", "health risk" and "health hazards", are introduced. In Sect. 3.2, health risk factors and their main parameters in built environments are further identified and classified into six groups: biological, chemical, physical, psychosocial, personal, and others. Detailed definition of health risk factors and their main parameters, followed by the results of epidemiological studies proving the association between potential health outcomes and health risk factors, are described in Sects. 3.3, 3.4, 3.5, 3.6 and 3.7. Identified and classified health risk factors and their parameters are the basis for the identification of single and multi-group interactions among them, described in Chap. 4.