In Six Sigma the Control Plan is required in the final phase of the project. Its purpose is to manage and sustain the success achieved in the Improve phase. To do this, the risks associated with the new solution are mitigated through measures. For example, risks identified through an FMEA in the Improve phase can be addressed with preventive actions in the Control phase. These actions are essentially tests for the risks. Typically, the Control plan specifies what, how, when, and who will test, as well as who is responsible and accountable, and what risks exist.

It is important that the tests focus on the risks associated with the solution concept. Often, the Control plan includes a before-and-after graphic of the main Y, with actions to be taken if Y falls below a certain threshold. However, this may not be sufficient for sustainability.