Regiment

The term came into use in Europe around the end of the 16th century, when armies transitioned from a collection of retinues following knights to a more formally organized structure.

In the British Army, the Regiment is for most purposes the largest "permanent" organisational unit. Above regimental level, organisation is changed to meet the tasks at hand. Because of their permanent nature, many regiments have long histories, often going back for centuries; the oldest British regiment still in existence is the Honourable Artillery Company, established in 1537, while the Royal Scots[?], formed in 1633, is the oldest infantry regiment. (These claims are contested on various points of precedence; see FAQ: Oldest Regiment in the British Army (http://www.regiments.org/milhist/about/questions/faq/oldest.htm).)

The United States Army was also once organized into regiments, but presently uses the brigade instead, except for cavalry. Although every battalion or squadron is associated with a regiment for historical purposes, the only combat regiments are cavalry regiments which are attached to a corps.