P&O (in full, The Peninsular and Oriental Steam Navigation Company is a British shipping and logistics company dating from the early 19th century.

In 1822, Brodie McGhie Willcox, a London ship broker, and Arthur Anderson, a sailor from the Shetland Isles, went into partnership to operate a shipping line, primarily operating routes between England and Spain and Portugal.The company flag colours are directly connected with the Peninsular flags: the white and blue represent the Portuguese flag in 1837, and the yellow and red the Spanish flag.

P&O first introduced passenger services in 1844, with a leisure cruise departing from Southampton to the Mediterranean.[2] These voyages were the first of their kind and the forerunner of modern cruise holidays.

In 1847, shortly after the Opium War, P&O entered the opium trade shipping 642,000 chests of Bengal and Malwa opium in the next eleven years.

Mail contracts were the basis of P&O's prosperity until the Second World War, but the company also continued to become a major commercial shipping line and passenger liner operator. In 1914, it took over the British India Steam Navigation Company, which was then the largest British shipping line, owning 131 steamers. In 1918, it gained a controlling interest in the Orient Line, its partner in the England-Australia mail route.​

After 1945, the passenger market declined to India, but boomed to Australia with the advent of paid-passages for literate and healthy European immigrants known as Ten Pound Poms.[6] P&O built 15 large passenger liners, including Himalaya, Chusan, Arcadia, and Iberia, culminating in Oriana and Canberra, which were an unprecedented speed and size.

P&O and Orient Line were formally merged in 1960 to form P&O-Orient Lines. In 1964, Orcades and Oronsay were transferred to the P&O fleet. The name Orient Line was dropped altogether in 1966 when Orsova and Oriana were also transferred to the P&O fleet.

In 1972, P&O formally absorbed the British-India Steam Navigation Company (BI). The amalgamation of these two companies began in 1914 but BI had retained its own identity until this time.