Just like cardboard boxes and pallets, these containers are a means to bundle cargo and goods into larger, unitized loads, that can be easily handled, moved, and stacked, and that will pack tightly in a ship or yard. Intermodal containers share a number of key construction features to withstand the stresses of intermodal shipping, to facilitate their handling and to allow stacking, as well as being identifiable through their individual, unique ISO 6346 reporting mark.

In 2012 there were about 20.5 million intermodal containers in the world of varying types to suit different cargoes. Containers have largely supplanted the traditional break bulk cargo – in 2010 containers accounted for 60% of the world’s seaborne trade. The predominant alternative methods of transport carry bulk cargo – either gaseous, liquid or solid – e.g. by bulk carrier or tank ship, tank car or truck. For air freight, the more light-weight IATA-defined unit load device is used.

Containers are transferred between rail, truck, and ship by container cranes at container terminals. Forklifts, reach stackers, straddle carriers, and cranes may be used to load and unload trucks or trains outside of container terminals. Swap bodys, sidelifters, tilt deck trucks, and hook trucks allow transfer to and from trucks with no extra equipment.

ISO-standard containers can be handled and lifted in a variety of ways by their corner fixtures, but the structure and strength of 45-foot (type E) containers limits their tolerance of side-lifting, nor can they be forklifted, based on ISO 3874 (1997).

Intermodal freight transport involves the transportation of freight in an intermodal container or vehicle, using multiple modes of transportation (rail, ship, and truck), without any handling of the freight itself when changing modes(without unpacking). Units can be secured in transit using “twistlock” points located at each corner of the container. Every container has a unique BIC code painted on the outside for identification and tracking, and is capable of carrying up to 20–25 metric tons. Costs for transport are calculated in twenty-foot equivalent units (TEU). The method reduces cargo handling, and so improves security, reduces damage and loss, and allows freight to be transported faster. Reduced costs over road trucking is the key benefit for inter-continental use. This may be offset by reduced timings for road transport over shorter distances.

When carried by rail, containers may be carried on flatcars or well cars. The latter are specially designed for container transport, and can accommodate double-stacked containers. However, the loading gauge of a rail system may restrict the modes and types of container shipment.

About 90% of non-bulk cargo worldwide is transported by container, and the largest container ships can carry over 19,000 TEU. Each year an estimated 10,000 shipping containers fall into the sea; of these 10% are expected to contain chemicals toxic to marine life.

Containers can also be transported in planes, as seen within intermodal freight transport. However, transporting containers in this way is typically avoided due to the cost of doing such and the lack of availability of planes which can accommodate such awkwardly sized cargo.