Continuous integration (CI) is the practice, in software engineering, of merging all developer working copies to a shared mainline several times a day. It was first named and proposed by Grady Booch in his 1991 method, although Booch did not advocate integrating several times a day. It was adopted as part of extreme programming (XP), which did advocate integrating more than once per day, perhaps as many as tens of times per day.