Continuous, or at least Continual, Improvement has become a major theme, perhaps the major theme, in manufacturing over the past 15 years and is certainly a core Lean concept. Although Kaizen has become well established since Masaaki Imai's classic work on the topic, it has become clear that there are two elements to improvement, namely continuous improvement and breakthrough improvement. Thus Juran refers to "breakthrough" activities, using "project by project" improvement, to attack "chronic" underlying quality problems as being different from more obvious problems. Davenport, in the context of business process reengineering, has referred to "the sequence of continuous alteration" between continuous improvement and more radical breakthroughs by reengineering. And Womack and Jones discuss "kaikaku" resulting in large, infrequent gains as being different from kaizen or continuous improvement resulting in frequent but small gains.

A traditional industrial engineering idea is that breakthrough or major event improvement activities are not continuous at all, but take place infrequently in response to a major change such as a new product introduction or in response to a "crisis". But during the past few years we have learned that effective breakthrough should be both proactive and frequent.

There are therefore four types of improvement, as shown in the figure. There is, or should be, a place for all four types in every organisation. Adopting lean manufacturing does not mean ignoring other forms of improvement to concentrate on kaizen and kaikaku. Passive approaches are a useful supplement and should continue. However, if all improvement is of the passive, reactive type the company may well slip behind.