They may be state-owned (particularly for port authorities) or privately run.
The work involves managing the movement of cargo containers between cargo ships, trucks and freight trains and optimizing the flow of goods through customs to minimize the amount of time a ship spends in port.
Maintaining efficiency involves managing and upgrading gantry cranes, berths, waterways, roads, storage facilities, communication equipment, computer systems and dockworkers' union contracts.
The port operator also manages paperwork, leases, safety and port security.
[1] This is a list of the world's largest port operators.