Advances in science and technology, the emergence of new diseases, globalization, and the changing nature of conflict have increased the risks posed by naturally occurring and man-made biological threats. From the anthrax letter attacks of 2001 to the H1N1 influenza pandemic in 2009, the 21st century has already witnessed several new biological threats emerge. Despite the diversity of biological threats and disagreement about the definition of biosecurity and the most urgent threats, the public health and national security communities must develop new capabilities, strategies and partnerships to address these new threats. A comprehensive definition of biosecurity that covers both naturally occurring and man-made biological threats is necessary to engage in multidisciplinary research, risk assessment, and policy-making. This talk will provide an overview of the spectrum of biological risks we face today, discuss the challenges to developing effective biosecurity strategies, and offer some thoughts on the future of biosecurity.