• All cosmetic products are composed of at least one, most often many, chemical substances. However, in many cases “ingredients” found in cosmetic products are not wholly identified in their exact molecular composition or structure. This chapter addresses and clarifies the questions of what constitutes a “cosmetic ingredient”; what legislative framework governs their manufacturing, sale, and use; and how can the industry (both the ingredient suppliers and the finished product formulators) cope with the requirements that differ widely around the world? Any cosmetic product may be formulated with any type of ingredient (single substance or blend) as long as the ingredient is not prohibited by a specific “negative” list. There are two sides to the legal obligations with respect to ingredients used in cosmetic products: the supplier’s side and the downstream user’s side (formulators). Cosmetic ingredients (substances or blends) are regulated as chemical substances, and thus fall under the legislation ruling manufacturing, handling, transport, and labeling of chemicals and, if applicable, hazardous or dangerous substances. Legal frameworks and requirements for the manufacturer (or importer) of cosmetic finished products are many, and widely differ from country to country.