The term “transportation” is used variously to designate the process, the means, or the systems whereby socially meaningful objects are conveyed through space. Transportation involves the relocating of such objects, by an energy-consuming mechanism, through an environmental medium; the social consequences of transportation may be both intended and unintended. This breadth of reference indicates a concept that is not easily definable, for it does not refer to a clearly delimited aspect of social reality. When the objects being transported are human beings, or when humans move by self-locomotion, in conceptual terms transportation merges with mobility. At another extreme, when objects are messages composed of meaningful symbols, transportation blends with communication. Perhaps this definitional ambiguity reflects the fact that transportation is the basic process by which direct physical contact and exchange among social units is attained and maintained. Given that transportation is a basic support to social organization and communication, it requires systematic organization in the interest of reliability. Scholars in various fields have been concerned with one or more of the elements involved in transportation: the character and distance of the space to be traversed; the technological and energy resources available for and actually in use; personnel and skills; motives, decision-making processes, and knowledge that bear on use, operation, and other related activities and decisions; the organizational characteristics of systems; and the diverse social consequences of system qualities and use.