As the complexity in the world increases due to increased interconnections, new communication technologies, and the widespread internet of things so too is the complexity of the public policy space changing. However, much of public policy analysis, formulation, analysis and monitoring and evaluation is being done like it was for the last 80 years or more since the beginning of the policy sciences as the formal study of public policy as a social science. Over the last 2- or 3-decades complexity science ideas have been increasingly applied in the social sciences to deal with social systems and other arenas of interest to public policy which displayed complex adaptive systems characteristics such as ecosystems. This has resulted in some refreshingly new ways of thinking of wicked policy problems and even in some new social science sub-disciplines like complexity economics. Yet a chasm exists between these developments and the use of complexity sciences in the teaching and practice of public policy. This chapter brings together in a selected way a lot that has been learned in the use of complexity thinking in public policy and summarizes the practical tools that can be used for policy and program design and evaluation in complex situations.