Six Sigma is a process improvement methodology pioneered by Motorola (initiated by engineer Bill Smith, known as the 'father of Six Sigma'). It became prominent through the success of General Electric, during the tenure of CEO Jack Welch who was an advocate for Six Sigma.
The methodology uses process improvement methods, with an emphasis on statistics to achieve a quality level of better than 3.4 defects per million opportunities. Key elements are:
In its classical form, Six Sigma is a project based approach, tackling projects that will return $100,000+ savings and take several months. Many companies now use an approach that involves more, but smaller, projects, and is less statistically intensive. These are often led by Green Belts rather than Black Belts.