The CMMI uses 5 Maturity Levels to characterize organizational improvement for sets of process areas.

CMMI Maturity Levels

Maturity means that whatever the company is doing, the company does it in a way that is well-documented, where everyone knows what is expected of them, where performance is not dependent on heroes, and where decisions are made on proper analysis of the situation.

Maturity Level 1: Initial
At maturity level 1, processes are usually ad hoc and chaotic. 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 chaos, maturity level 1 organizations often produce products and services that work; however, they frequently exceed their budgets and do not meet their timelines.

Maturity Level 2: Managed
At maturity level 2, the projects of the organization have ensured that processes are planned and executed according to plan. These basic project management processes may be different for each particular project.
The projects employ skilled people who have adequate resources to produce controlled outputs; which are monitored, controlled, and reviewed; and are evaluated for compliance to their process descriptions. The process discipline reflected by maturity level 2 helps to ensure that existing practices are retained during times of stress. When these practices are in place, projects are performed and managed according to their documented plans.

Maturity Level 3: Defined
At maturity level 3, processes are described on an organizational level, and these are used to establish consistency across the organization and makes it easy to learn from each other.
Projects create their defined processes by tailoring the organization’s set of standard processes with help of tailoring guidelines.
Another critical distinction is that at maturity level 3, processes are typically described more rigorously than at maturity level 2. At maturity level 3, processes are managed more proactively using an understanding of the interrelationships of the process activities and detailed measurements of the process, their work products, and services.

Maturity Level 4: Quantitatively Managed
At maturity level 4, the organization and projects establish quantitative goals for quality and process performance and use them as criteria in management processes.
For selected sub-processes, detailed measurements of process performance are collected and statistically analyzed. Special causes of process variation are identified and, where appropriate, the sources of process variation are corrected to prevent future occurrence.

Maturity Level 5: Optimizing
Maturity level 5 focuses on continually improving process performance through incremental and innovative process and technological improvements.
The effects of deployed process improvements are measured and evaluated against quantitative process improvement goals.
At maturity level 5, the organization is concerned with addressing common causes of process variation and improving the process (to shift the mean of the process performance or reduce the process variation).