Book excerpt: Slightly more than 100,000 chemicals are produced in such an amount that they are threatening to the environment. These include common chemicals such as household cleaners, detergents, cosmetics, medicines, and pesticides. The Handbook of Estimation Methods in Ecotoxicology and Environmental Chemistry presents estimation methods for determining a number of physicochemical, biological, and toxicological parameters for these chemicals. Included is WinTox software, an estimation tool that is quick and easy to use; it provides a good initial estimate that can be further refined. Through the estimation methods demonstrated in this book, the following urgent questions can be answered: