The fourth of the five-lean-principles: let the customer pull value from the producer. Instead of pushing products based on forecasts and production schedules, produce only what the next downstream step needs, when it needs it.
The Principle
james-p-womack and daniel-t-jones position pull as the mechanism that connects production to actual demand. In lean-thinking, they argue that once flow is established, the organization can let the customer's actual demand propagate backward through the value stream, triggering production only when needed. This eliminates the waste of overproduction — which taiichi-ohno considered the worst of the seven wastes because it generates all the others (inventory, waiting, transportation, etc.).
TPS Source
Ohno's kanban system was the operational mechanism for pull at toyota-motor-corporation. A kanban (signal card) attached to a container of parts would be sent upstream when the downstream process consumed those parts, triggering production of exactly that quantity. The system was elegant in its simplicity: no central scheduling, no forecasting — just a physical signal propagating demand information backward through the production chain.
Womack and Jones abstract pull from kanban's physical mechanism to a general principle: design systems so that nothing is produced upstream until the customer downstream signals a need. This abstraction enables application to information products, services, and processes where physical kanban cards don't apply — but it also loses the specific disciplining mechanism that made pull work at Toyota. Without kanban's physical constraints, "pull" can become an aspiration rather than an operational reality.
Relationship to Flow
Pull and flow are deeply interdependent in TPS. Flow makes pull possible (if work doesn't flow, pull signals can't propagate); pull disciplines flow (without demand signals, continuous flow produces overproduction). Womack and Jones present them as sequential steps 3 and 4, but in practice they must be implemented together. This is one of the points where the sequential framing of the five-lean-principles simplifies TPS's simultaneous, interlocking structure.