Consider scheduling tasks on dedicated processors or machines. We assume that tasks belong to a set of n jobs, each of which is characterized by the same machine sequence. For convenience, let us assume that any two consecutive tasks of the same job are to be processed on different machines. The type of factory layout in the general case — handled in Chapter 8 — is the job shop; the particular case where each job is processed on a set of machines in the same order is the flow shop. A part of this chapter will also consider the situation where no predefined machine or processor sequences are existing. This results in the case of scheduling a set of jobs on a set of machines in any order — the open shop. The most commonly used performance measure will be makespan minimization.