This chapter discusses the universal concept of a system through the lens of system thinking and science and applies it to the concept of sustainable development. Because system science is inherently multidisciplinary, examples and concepts are borrowed from many disciplines. Any system can be explained through multiple dimensions or components of which this chapter details structure' by modeling systems as static cross-impact networks; it frames sustainable developmentreferred to as anthropocentric systemsas an interconnected group of sectors, like an economy, using a nexus approach. As nations work toward implementing the complex and interconnected United Nation's Sustainable Development Goals (SDGs), this chapter offers methods to identify the type of interactions and quantify the strengths among them. This approach supports the process of priority setting and highlights areas in particular needed for policy coordination across different sectors.