Design For Six Sigma (D.F.S.S.) is a methodological theory that links different areas of knowledge, not necessarily engineering, and aims to develop designs for new processes or products that are optimal in terms of fully satisfying the requirements of the end customer.

The term ‘Six Sigma’ in the ‘Lean Six Sigma’ methodology for improving existing processes and products is defined as the level at which so-called possible conceptual or operational product vulnerabilities also known as Critical to Quality or Critical to Satisfaction (CTQ or CTS) are minimized at project level.

D.F.S.S. in particular is based on particular project methodologies, such as the Axiomatic Design and the Theory of Inventive Problem Solving (commonly identified with TRIZ), and on a wide range of quantitative (e.g. Hypothesis Testing) or qualitative (e. g. DFMEA) statistical tools that allow, starting also from empirical assessments of the Customer’s requirements and prototyping or process or product simulations through approaches such as Design Of Experiment (DOE), to realize, by means of approaches such as Design Of Experiment (DOE), a process or product simulation. g. DFMEA) that allow, starting also from empirical evaluations of the Customer’s requests and prototyping or process or product simulations through approaches such as Design Of Experiment (DOE), to realize samples that show to be “designed it right first time”. (‘design it right the first time’), making it unlikely that these will be returned to after production. The purely ‘proactive’ approach of the DFSS versus the methodologically unstructured ‘reactive’ (firefighting) approach to design therefore remains clear.