Seeds of Algebraic Thinking comes from the Knowledge in Pieces (KiP) perspective of learning. KiP is a systems approach to learning that stems from the constructivist idea that people learn by building on prior knowledge. As people experience the world, they acquire small, sub-conceptual knowledge elements. When people engage in a particular context, these sub-conceptual resources get elicited and organized in ways that are potentially productive in that situation. This article summarizes the theory behind Seeds of Algebraic Thinking, how they connect to formal algebraic reasoning, and how they can be leveraged during classroom instruction.