Natural products have been used throughout history as a source of medicines.A large number of currently used antibiotics and anti-tumor agents are either derived directly from natural sources or are inspired by natural products.New knowledge on cancer molecular biology and genetics as well as advances in instrumentation are challenging the existing paradigm of drug screening and development processes, and costs for drug development have grown substantially in recent years.Sharing knowledge and leveraging costs are key elements of success.The NCI has been supporting natural products-based cancer drug discovery programs for more than 50 years.