plan, do, check, adjust

thumb|right|The plan–do–check–act cycle PDCA (plan–do–check–act), sometimes called plan–do–check–adjust is an iterative design and management method used in business for the control and continual improvement of processes and products. It is also known as the Shewhart cycle, or the control circle/cycle. Another version of this PDCA cycle is OPDCA. The added stands for observation or as some versions say: "Observe the current condition." This emphasis on observation and current condition has currency with the literature on lean manufacturing and the Toyota Production System. The PDCA cycle, with Ishikawa's changes, can be traced back to S. Mizuno of the Tokyo Institute of Technology in 1959.

The PDCA cycle is also known as PDSA cycle (where S stands for study). It was an early means of representing the task areas of traditional quality management. The cycle is sometimes referred to as the Shewhart / Deming cycle since it originated with physicist Walter Shewhart at the Bell Telephone Laboratories in the 1920s. W. Edwards Deming modified the Shewhart cycle in the 1940s and subsequently applied it to management practices in Japan in the 1950s.