System dynamics provides the basic building blocks necessary to construct models that teach us how and why complex real-world systems behave the way they do over time. For us, the goal is to leverage this added understanding to design and implement more efficient and effective policies. This chapter introduces the concept of time paths and how to begin looking at the world in terms of changing patterns over time rather than as static snap-shot events. This chapter also introduces the concept of system stocks, system flows, and system feedback. To understand the dynamic behavior of a system, its key physical and information stocks, flows and feedback structures must be identified.