This tutorial deals with runtime enforcement and advocates its use as an extension of runtime verification. While research efforts in runtime verification have been mainly concerned with detection of misbehaviors and acknowledgement of desired behaviors, runtime enforcement aims mainly to circumvent misbehaviors of systems and to guarantee desired behaviors. First, we propose a comparison between runtime verification and runtime enforcement. We then present previous theoretical models of runtime enforcement mechanisms and their expressive power with respect to enforcement. Then, we overview existing work on runtime enforcement monitor synthesis. Finally, we propose some future challenges for the runtime enforcement technique.