Questions and answers

Kaizen and Lean: the common questions, answered with sources

By KaizenProof · Updated 9 October 2026 · Last reviewed 9 October 2026

In short

Kaizen is a Japanese word for improvement which, in management, has come to mean improving work continuously through small changes made by the people who do it; Lean is the name researchers gave in 1988 to the way Toyota organises production. Neither has a single inventor or a single founding date. [15][20]

The sixteen answers below are short enough to quote and each lists the sources it rests on. Where the usual answer is disputed, the answer says so.

Questions

What does the word kaizen mean?

Kaizen (改善) is a Japanese word meaning improvement, or change for the better. In everyday Japanese it carries no sense of continuous and no sense of a philosophy. In management it has come to mean improving work continuously through many small changes made by the people who do the work. [5][15]

Who invented Kaizen?

No single person. The practice grew in Japanese companies during and after the post-war occupation, drawing on American supervisor training and on the teaching of quality control, and Toyota made it part of daily work. Masaaki Imai gave it its name in Western management with his 1986 book Kaizen: The Key to Japan's Competitive Success. [13][15][16]

Did W. Edwards Deming bring Kaizen to Japan?

Not Kaizen as such. Deming taught statistical quality control to Japanese engineers and managers in the summer of 1950, at the invitation of the Union of Japanese Scientists and Engineers, which went on to establish the Deming Prize in his honour. His teaching is one root of Japanese quality management; the small-step improvement habit has other roots as well, including the American programme Training Within Industry. [12][15][16][17]

Who created the Toyota Production System?

Toyota's own account credits four people: Sakichi Toyoda, whose self-stopping looms gave the idea of jidoka; Kiichiro Toyoda, who argued for just-in-time; Eiji Toyoda, who put both into practice; and Taiichi Ohno, who built the framework. It was developed over decades and not invented at once: Toyota's chronology puts the foundations in the late 1940s and early 1950s and the start of implementation at all its plants in 1960. [1][3]

What are the two pillars of the Toyota Production System?

Jidoka and just-in-time. Jidoka, which Toyota translates as automation with a human touch, means stopping the work as soon as something is abnormal. Just-in-time means making only what is needed, when it is needed, in the amount needed. The Toyota Way, a separate statement of values written down in 2001, has two different pillars: continuous improvement and respect for people. [1][2]

Who coined the term lean?

John Krafcik, then a graduate student at the Massachusetts Institute of Technology, in his 1988 article Triumph of the Lean Production System, published in Sloan Management Review. The term became widely known through the 1990 book The Machine That Changed the World, by James Womack, Daniel Jones and Daniel Roos. [14][20][21][22]

Is Lean the same as the Toyota Production System?

Not exactly. The Toyota Production System is Toyota's own system, which the company describes through two pillars, jidoka and just-in-time. Lean is the description of that system made by outside researchers in 1988 and 1990 and then generalised, in 1996, into five principles meant for any organisation. [1][4][20]

What are the five principles of Lean?

Value, the value stream, flow, pull and perfection. In order: specify what the customer values, map the steps that deliver it, make the work flow through those steps, let customer demand pull the work, and keep improving. James Womack and Daniel Jones set them out in the book Lean Thinking in 1996. [4][21]

Are there seven wastes or eight?

Seven in the original list, eight in most current teaching. The seven, as the Lean Enterprise Institute lists them and credits them to Taiichi Ohno, are overproduction, waiting, conveyance, processing, inventory, motion and correction. Many lists, ours included, call conveyance transportation, processing extra-processing, and correction defects. The eighth, people's unused skills, was added by later writers and has no agreed author; Wikipedia's article on muda cites Jeffrey Liker's 2004 book The Toyota Way for it. [6][19][20]

What are muda, mura and muri?

They are three Japanese words for what the Toyota Production System sets out to remove. Muda is waste: activity that adds nothing the customer needs. Mura is unevenness in the flow of work. Muri is overburden: asking more of people or equipment than they can reasonably give. [1][18]

Who invented the 5 Whys?

It is usually credited to Sakichi Toyoda, the founder of the Toyoda loom business. The written source is Taiichi Ohno, whose book on the Toyota Production System describes asking why five times, with the example of a stopped machine traced back to a missing strainer. The careful statement is that Ohno described the practice in writing; the sources we opened do not show where the credit to Sakichi Toyoda comes from. [7][23]

Who invented PDCA, and is it the same as PDSA?

PDCA has no single author. It descends from Walter Shewhart's three-step cycle of 1939 and the four-step wheel W. Edwards Deming showed in Japan in 1950; the plan-do-check-act wording appeared in Japan in 1951. PDSA, plan-do-study-act, is Deming's own later version, published in 1993. He did not accept PDCA as his, so calling PDCA the Deming cycle is common but not accurate. [11]

What do the five S of 5S stand for?

Seiri, seiton, seiso, seiketsu and shitsuke, usually translated as sort, straighten, shine, standardise and sustain. The Lean Enterprise Institute notes that Toyota traditionally speaks of only four S, leaving out the last, and that some practitioners add a sixth for safety. [8]

What does kanban mean?

Kanban is Japanese for sign or signboard. In the Toyota Production System a kanban is a signal, often a card, that authorises the previous step to make or move a set quantity. Taiichi Ohno developed it after Toyota studied how supermarkets restock shelves, and Toyota applied it in its main plant machine shop in 1953. [9][24]

Why is an A3 report called an A3?

It is named after the paper it is written on: A3, a sheet of 297 by 420 millimetres. The Lean Enterprise Institute describes the A3 report as a practice pioneered at Toyota of putting the problem, the analysis, the corrective actions and the action plan on that single sheet. [10]

What is a Kaizen event?

A Kaizen event, also called a kaizen blitz or kaizen workshop, is a team set aside for a few days, commonly five, to study one process and put a significant improvement in place before the event ends. It is one way of doing Kaizen; the other is daily Kaizen, small changes made as part of normal work. [5]

How were these answers checked?

Each answer was written from the sources numbered under it, and every source was opened and compared with the text on the review date shown at the top of the page. We preferred a company's or an institute's own page to a summary of it, and we name Wikipedia where it is the source. An answer never states a year or credits a person without one.

Several of these questions have no clean answer, because the usual story was written decades after the events. The page on the history of Kaizen and Lean sets out what is disputed and who says what. For definitions, use the Kaizen glossary; for when to use each method, the Lean methods reference; for the books these answers cite, the reading list.

Sources

Each numbered source was opened and compared with the text of this page on 9 October 2026. A number in square brackets after a statement points to the source it rests on.

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