Parallel execution time is expected to decrease as the number of processors increases. We show in this chapter that this is not as easy as it seems, even for perfectly parallel applications. In particular, processors are subject to faults. The more processors are available, the more likely faults will strike during execution. The main strategy to cope with faults in High Performance Computing is checkpointing. We introduce the reader to this approach, and explain how to determine the optimal checkpointing period through scheduling techniques. We also detail how to combine checkpointing with prediction and with replication.