This volume in the AAPS Advances series covers various quality, safety and clinical aspects of drug development that are relevant to new and/or generic drugs containing a complex mixture of molecules. Specific topics discussed include: raw materials sourcing; manufacturing controls; characterization; identification of critical product quality components and attributes; identification of impurities, particularly as they bear on toxicity and immunogenicity; clinical trial study design considerations, and the regulatory science applications to development of such complex mixtures. Complex mixtures are challenging to characterize and analyze using standard methods. Further challenges extend throughout the product development cycle from raw material control to clinical study design.  The regulatory landscape is rapidly changing as new types of complex mixtures are introduced into clinical trials and to the market (e.g., traditional Chinese medicines and medical marijuana products), while older products are facing generic competition for the first time (e.g., enoxaparin). The future outlook for complex generic drug products, as opposed to the more commonly developed targeted single agent drug products is not clear.  The risks pertaining to lack of a full understanding of raw material control, process and controls in manufacture, as well as characterization of a complex mixture were seen vividly during the heparin crisis of 2008. As such powerful lessons have been learned about the regulatory science specific to complex products. The Science and Regulations of Naturally Derived Complex Drugs addresses the interests among industry, academics, and government on the issues surrounding the future development of mixtures for medicinal use.