Processes that definitely got stuck in the operational sequence without regular measures for the synchronization with other processes being the cause are called jammed. “Definitely” means that any continuation of their execution is impossible; particularly, they cannot be unblocked. A state in which processes are jammed in this way is called a deadlock. In this chapter, such states are characterized and illustrated by simple examples. Measures for their prevention and for their detection and recovery are discussed; and to avoid them, the banker’s algorithm of Dijkstra is presented. Finally, the blocking probabilities are calculated, and all countermeasures are evaluated.