What is CMM and different levels? explain?

The Capability Maturity Model (CMM) is a process capability maturity model which aids in the definition and understanding of an organization's processes.

The CMM was originally described in the book Managing the Software Process (Addison Wesley Professional, Massachusetts, 1989). The CMM was conceived by Watts Humphrey, who based it on the earlier work of Phil Crosby. Active development of the model by the SEI (US Dept. of Defense Software Engineering Institute) began in 1986. The SEI was at Carnegie Mellon University in Pittsburgh.

The CMM was originally intended as a tool for objectively assessing the ability of government contractors' processes to perform a contracted software project. Though it comes from the area of software development, it can be (and has been and still is being) applied as a generally applicable model to assist in understanding the process capability maturity of organizations in diverse areas. For example, software engineering, system engineering, project management, risk management, system acquisition, information technology (IT), personnel management. It has been used extensively for avionics software and government projects around the world.

The CMM has been superseded by CMMI (Capability Maturity Model Integration). The old CMM was renamed to Software Engineering CMM (SE-CMM) and organizations accreditations based on SE-CMM expired on 31 December 2007.

Other variants of the CMM include Software Security Engineering CMM SSE-CMM and People CMM. Other maturity models such as ISM3 have also emerged.