CMM(Capability Maturity Model)

The Capability Maturity Model (CMM), also known as the Software CMM (SW-CMM), was first described by Watts Humphrey in his book Managing the Software Process. The CMM is a process model based on software best-practises effective in large-scale, multi-person projects.
The CMM has been retired and not been updated in over 10 years. CMM has been superseded by CMMI (Capability Maturity Model Integration).
The CMM has been used to assess the maturity levels of organisation areas as diverse as software engineering, system engineering, project management, risk management, system acquisition, information technology (IT) or personnel management, against a scale of five key processes, namely: Initial, Repeatable, Defined, Managed and Optimised.
CMM was developed by the Software Engineering Institute (SEI) at Carnegie Mellon University in Pittsburgh. It has been used extensively for avionics software and government projects around the world.
Currently, some government departments require software development contract organisations to achieve and operate at a level-3 standard Maturity model
The Capability Maturity Model (CMM) is a way to develop and refine an organization's processes. The first CMM was for the purpose of developing and refining software development processes. A maturity model is a structured collection of elements that describe characteristics of effective processes. A maturity model provides:

1. a place to start the benefit of a community’s prior experiences 
2. a common language and a shared vision 
3. a framework for prioritising actions 
4. a way to define what improvement means for your organization. 
5. A maturity model can be used as a benchmark for assessing different organizations for equivalent comparison. The model describes the maturity of the company based upon the project the company is handling and the related clients
6. Levels of the CMM

Level 1 - Initial
At maturity level 1, processes are usually ad hoc, and the organization usually does not provide a stable environment. Success in these organizations depends on the competence and heroics of the people in the organization, and not on the use of proven processes. In spite of this ad hoc, chaotic environment, maturity level 1 organizations often produce products and services that work; however, they frequently exceed the budget and schedule of their projects.
Maturity level 1 organizations are characterised by a tendency to over commit, abandon processes in the time of crisis, and not be able to repeat their past successes again.
Level 1 software project success depends on having high quality people
Level 2 - Repeatable [Managed]
At maturity level 2, software development successes are repeatable. The processes may not repeat for all the projects in the organization. The organization may use some basic project management to track cost and schedule.
Process discipline helps ensure that existing practises are retained during times of stress. When these practises are in place, projects are performed and managed according to their documented plans.
Project status and the delivery of services are visible to management at defined points (for example, at major milestones and at the completion of major tasks).
Basic project management processes are established to track cost, schedule, and functionality. The minimum process discipline is in place to repeat earlier successes on projects with similar applications and scope. There is still a significant risk of exceeding cost and time estimates
Level 3 - Defined
The organization’s set of standard processes, which are the basis for level 3, are established and improved over time. These standard processes are used to establish consistency across the organization. Projects establish their defined processes by applying the organization’s set of standard processes, tailored, if necessary, within similarly standardised guidelines.
The organization’s management establishes process objectives for the organization’s set of standard processes, and ensures that these objectives are appropriately addressed.
A critical distinction between level 2 and level 3 is the scope of standards, process descriptions, and procedures. At level 2, the standards, process descriptions, and procedures may be quite different in each specific instance of the process (for example, on each particular project). At level 3, the standards, process descriptions, and procedures for a project are tailored from the organization’s set of standard processes to suit a particular project or organisational unit
Level 4 - Quantitatively Managed
Using precise measurements, management can effectively control the software development effort. In particular, management can identify ways to adjust and adapt the process to particular projects without measurable losses of quality or deviations from specifications. Organisations at this level set quantitative quality goals for both software process and software maintenance. Sub processes are selected that significantly contribute to overall process performance. These selected sub processes are controlled using statistical and other quantitative techniques. A critical distinction between maturity level 3 and maturity level 4 is the predictability of process performance. At maturity level 4, the performance of processes is controlled using statistical and other quantitative techniques, and is quantitatively predictable. At maturity level 3, processes are only qualitatively predictable
Level 5 - Optimising
Maturity level 5 focuses on continually improving process performance through both incremental and innovative technological improvements. Quantitative process-improvement objectives for the organization are established, continually revised to reflect changing business objectives, and used as criteria in managing process improvement. The effects of deployed process improvements are measured and evaluated against the quantitative process-improvement objectives. Both the defined processes and the organization’s set of standard processes are targets of measurable improvement activities.
Process improvements to address common causes of process variation and measurably improve the organization’s processes are identified, evaluated, and deployed
Six Sigma
Six Sigma is a disciplined, data-driven approach and methodology for eliminating defects (driving towards six standard deviations between the mean and the nearest specification limit) in any process -- from manufacturing to transactional and from product to service.
The fundamental objective of the Six Sigma methodology is the implementation of a measurement-based strategy that focuses on process improvement and variation reduction through the application of Six Sigma improvement projects. This is accomplished through the use of two Six Sigma sub-methodologies:
DMAIC
The Six Sigma DMAIC process (define, measure, analyse
DMADV
The Six Sigma DMADV process (define, measure, analyse, design, verify) is an improvement system used to develop new processes or products at Six Sigma quality levels. It can also be employed if a current process requires more than just incremental improvement.