Lean Thinking - usually just called 'Lean' - is a way of achieving more with fewer resources. It is based on the concept that anything which does not add value is wasteful, and seeks to prevent the use of resources for anything other than the creation of added value.
At the core of Six Sigma is the methodology to define, measure, analyse, improve and control (DMAIC).
Lean involves numerous methods of working, rather than different tools.
Lean Six Sigma
Many businesses use either Lean or Six Sigma but an increasing number choose Lean Six Sigma, which uses tools from both methodologies.
This calls for a particularly disciplined approach, and it is essential to fit the tools to the project, rather than the other way round. Some projects are better suited to Lean, while others are best served by Six Sigma.
Lean Six Sigma uses the two methodologies to interact with and reinforce one another. This is because, in certain businesses, better results can be achieved by a combination of Lean's productivity improvements and the quality benefits of Six Sigma. For example, if you are deploying Six Sigma using the DMAIC methodology, you may find that a Lean system - such as 'Just In Time' - could be used at the 'Improve' stage.