Six Sigma is a business management strategy , to improve the quality of process outputs by identifying and removing the causes of defects (errors) and minimizing variability in manufacturing and business processes. It uses a set ofquality management methods, including statistical methods, and creates a special infrastructure of people within the organization ("Black Belts", "Green Belts", etc.) who are experts in these methods. Each Six Sigma project carried out within an organization follows a defined sequence of steps and has quantified targets. These targets can be financial (cost reduction or profit increase) or whatever is critical to the customer of that process (cycle time, safety, delivery etc.)

Six Sigma at many organizations simply means a measure of quality that strives for near perfection. 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 statistical representation of Six Sigma describes quantitatively how a process is performing. To achieve Six Sigma, a process must not produce more than 3.4 defects per million opportunities. 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 and DMADV. The Six Sigma DMAIC process (define, measure, analyze, improve, control) is an improvement system for existing processes falling below specification and looking for incremental improvement. The Six Sigma DMADV process (define, measure, analyze, 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. Both Six Sigma processes are executed by Six Sigma Green Belts and Six Sigma Black Belts, and are overseen bySix Sigma Master Black Belts.

    According to the Six Sigma Academy, Black Belts save companies approximately $230,000 per project and can complete four to 6 projects per year. General Electric, one of the most successful companies implementing Six Sigma, has estimated benefits on the order of $10 billion during the first five years of implementation. GE first began Six Sigma in 1995 after Motorola and Allied Signal blazed the Six Sigma trail. Since then, thousands of companies around the world have discovered the far reaching benefits of Six Sigma.

Quality management tools and methods used in Six Sigma

    Within the individual phases of a DMAIC or DMADV project, Six Sigma utilizes many established quality-management tools that are also used outside of Six Sigma. The following table shows an overview of the main methods used.

- 5 Whys	- Analysis of variance	- ANOVA Gauge R&R
- Axiomatic design	- Business Process Mapping	- Catapult exercise on variability
- Cause & effects diagram	- Chi-square test of independence and fits	- Control chart
- Correlation	- Cost-benefit analysis	- CTQ tree
- Taguchi Loss Function	- Design of experiments	- Thought process map
- General linear model	- Histograms	- Homoscedasticity
- Taguchi methods	- Pareto chart	- Pick chart
- Process capability	- Regression analysis	- Root cause analysis
- Run charts	- Quantitative marketing research through EFM sys	- Stratification
- Quality Function Deployment (QFD)	- SIPOC analysis (Suppliers, Inputs, Process, Outputs, Customers)	- Failure mode and effects analysis (FMEA)
- TRIZ