The Australian Shepherd was developed from Spanish dogs to create a sheep herder on the ranches. They were transported to the United States with the colonies and most likely crossed with collie lines upon arrival. Today Australian Shepherds are used for a variety of jobs including herding, police work, agility and obediance trailing, guarding, search and rescue, and many more.
http://www.australianshepherds.org/akcbreedstandard.html
http://www.dogbreedinfo.com/australianshepherd.htm
http://allaboutaussies.wordpress.com/2008/08/15/why-are-aussie%E2%80%99s-tails-docked/