It is very important to understand that Reengineering is not a separate discipline. It is, in fact, a subset of TQM. The essential difference between (Business Process) Reengineering and TQM is that reengineering aims at quantum gains on the order of 30 to 50 percent or more, whereas Total Quality Management programs stress incremental progress, striving for inch-by-inch gains again and again.
The two approaches to improve performance are not mutually exclusive; it makes sense to use them in tandem. Reengineering can be used to first produce good basic design that dramatically improves a business process. Total quality programs can be used to work out bugs, perfect the processes, and gradually improve both efficient and effectiveness.
Such two-pronged approach to implementing organizational and strategic change is like a marathon race where you run fast four laps as fast as you can, then gradually pick up speed the remainder of the way.
Source: Strategic Management, 10 the Edition by Thmpson Strikeland