Chemical substances, physical agents and built structures exhibit various types of hazard due to their inherent toxic, mutagenic, carcinogenic, reprotoxic and sensitizing character or damaging to the immune and hormone system. The first steps in managing an environment contaminated by chemical substances are characterization of hazards and quantification of their risks. Chemical models — using only analytical data — are still the most widely used applications for assessing potential adverse effects and the fate and behavior of chemicals in the environment. Chemical models rely on the assumption that the adverse effect is proportional to the concentration, which in most cases is incorrect. In this volume, other models such as biological and ecological or regression models are discussed in detail and compared.