The Girl Guide movement shares its roots with the Boy Scout movement that was founded by Baden-Powell during the South African War of 1899-1902. During the war Baden-Powell, a British officer enlisted boys to act as messengers and organised these messengers into patrols. Each patrol had a leader.
This scheme was so successful that on his return to England, he decided to continue the programme to teach young boys the skills of camping, teamwork, pioneering, leadership, pioneering and stalking. Powell was pleasantly surprised at a scout rally at Crystal Palace in 1909, when a significant number of girls, dressed as scouts attended. He then realised that he should start a similar movement for girls. The name 'Girl Guides' came from Powell's experiences in India, where a group of men, who went by the name 'Guides' undertook dangerous expeditions in the North-West frontier.
The name 'Girl Guides' was decided upon as the title of these pioneering young women. Powell, together with his sister, Agnes wrote the Girl Guide Handbook, which was called 'How Girls can help build up the Empire". On 31 May 1910, the Girl Guides were formed with Agnes Baden-Powell as the First President of the Girl Guides movement.
References:
Girl Guides International History (online), available at: http://www.girlguides.org.sg [Accessed 17 May 2010]
Some Aspects of Lord Baden-Powell and the Scouts at Modderfontein (online), available at: http://samilitaryhistory.org [Accessed 17 May 2010]