We explain the rationale for congestion charges in congested cities. We review the existing congestion charging systems in the world and their design. We show that congestion charges have proven to be efficient in reducing congestion in the long run. Hence, it works. However, we also show that congestion reduction cannot be taken for granted, it demands a good design of the system. A poor system design can easily deteriorate the traffic situation, by causing second-best problems. To develop an efficient system design, using a good, calibrated state-of-practice transport model is key. We end the chapter by discussing why are congestion charges so rare in the world. This has mainly to do with difficulties of building long-term public and political support. These depend to a large extent on the power over the revenues.