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James Womack and Dan Jones are the founders of the Lean Enterprise Institute and the Lean Enterprise Academy (UK), respectively. Their book, Lean Thinking: Banish Waste and Create Wealth in Your Corporation, is considered by some to be the bible of Lean Manufacturing. It was initially published in 1996 based on their in-depth study of Toyota’s fabled Toyota Production System (TPS).

Womack and Jones realized that every business output results from a process. Process thinking in operations management requires leaders and workers to view the organization as a set of related processes that work together for a common goal rather than a group of departments supporting a specific function.
These ideas are widely used by organizations in every sector to better design, track, and optimize business operations. Companies have not done away with functional departments. Instead, they view the work departments do differently. Departments don't exist on their terms. Each receives inputs from other functions and provides outputs that other departments must consume to complete their work.

In short, each function or person contributes to one or more business processes. So, instead of managing departments, process thinking means managing entire operations. A process might move through a series of teams or functions, each with its requirements, but the purpose of each one is to create value for the customer, which is what matters.