Six Sigma

Six sigma is an overall quality (and business) improvement initiative, originally popularized by Motorola. It utilizes a four step improvement process.
Measure:    Identify customer needs and quantity defect levels.
Analyze:     Determine root causes of defects.
Correction: Permanently eliminate root causes.
Control:      Maintain gains over time.

It is being applied to all processes, including non-manufacturing processes, such as finance, accounting, human resources, sales etc. Hence, Six Sigma provides an overall road map to help practicioners to integrate various tools into an overall approach to improvement.