This book contains 20 papers drawn from presentations and discussions at the NATO Advanced Research Workshop on Complex Societal Dynamics: Security Challenges and Opportunities, held in Zagreb, Croatia in December 2009. The theory of complex systems views societies as complex configurations of actors engaged in overlapping and interlocking patterns of relationship. While the rapid development of computing capabilities has provided the tools to study complex systems in a controlled, repeatable and rigorous manner, these are rarely applied to the security domain, and security experts are not ade.