In ancient times runners and homing pigeons were used to deliver timely messages. When the horse became domesticated its use was rapidly adopted by couriers.

A courier is a person or company employed to deliver messages, packages and mail. Couriers are distinguished from ordinary mail services by features such as speed, security, tracking, signature, specialization and individualization of services, and committed delivery times, which are optional for most everyday mail services.

As a premium service, couriers are usually more expensive than usual mail services, and their use is typically restricted to packages where one or more of these features are considered important enough to warrant the cost.

Different courier services operate on all scales, from within specific towns or cities, to regional, national and global services. The world's largest courier companies are UPS, followed by FedEx and DHL, the first two being based in the United States and the latter now owned by Deutsche Post, a German company, and offer services worldwide, typically via a hub and spoke model.

In cities, there are often bicycle couriers or motorcycle couriers but most couriers today use trucks and aircraft. Owner Drivers operate alone or in small groups, covering both regular routes and often undertake 'overflow' work from larger courier companies and major integrators.

Definition:

a person who carries a message

A messenger sent with haste to convey letters or dispatches, usually on public business.

A messenger, especially one on official diplomatic business.

A spy carrying secret information.