This is an individual chapter of Theory of Constraints Handbook. The purpose of this chapter is to show how the Theory of Constraints (TOC) is used to improve the performance of a company while positively contributing to improving its supply chain. The key to becoming an agile company, better responding to the continuously changing demands of your customers, is having the capability to quickly respond to inevitable market fluctuations. One way to accomplish this is by taking a systems approach to leverage proven process improvement tools and thinking such as TOC, Lean and Six Sigma. This will result in a systems architecture that will guide and influence the way the company is managed. The change in the company will be profound and like any improvement, some people will resist the need to change. So a central component of achieving this required change will be developing and effectively implementing an aggressive paradigm shift with full participation from the top level of leadership in the company. Regrettably, in the past there have been many failed improvement attempts that ignored this. Erroneously, the conclusion was that the process improvements themselves were flawed. The failing was the company or their trusted advisors did not understand how they should be properly used. In most cases, the improvements were implemented within the company in isolation and without understanding the impact on their supply chain.