The atlatl is a sophisticated combination hunting tool or weapon, formed out of a short dart with a point socketed into a longer shaft. A leather strap hooked at the far end allowed the hunter to fling the atlatl over her shoulder, the pointed dart flying off in a deadly and accurate manner, from a safe distance. Sometimes people use the word to refer solely to the wooden extension shaft; others use it to refer to the entire segmented tool, dart point, shaft, and leather strap.
The atlatl was invented by Homo sapiens during the Upper Paleolithic period, about 21,000 to 17,000 years ago. The earliest secure data concerning atlatls has come from several caves in France dating to the Upper Paleolithic. The very earliest atlatl shaft found to date is a simple antler hook dated to the Solutrean period (about 17,500 years ago), recovered from the site of Combe Sauniere.
More details on atlatl history and function can be found in the Raging Cow article on atlatl throwing contests.
Butler, B. R. 1977 Atlatl functions, fancy, flex, and fun. A reply to Howard. Plains Anthropologist 22(76):161-162.
Butler, B. R. 1980 Penetrating elephant hide with wood atlatl darts. Plains Anthropologist 25(90):353-356.
Butler, William B. 1975 The atlatl: The physics of function and performance. Plains Anthropologist 20(68):105-110.
Howard, Calvin D. 1976 Atlatl function: A reply to Butler. Plains Anthropologist 21(74):313-314.
Kennedy, Kenneth A. R. 2004 Slings and arrows of predaceous fortune: Asian evidence of prehistoric spear use. Evolutionary Anthropology 13(4):127-131.
Patterson, Leland W. 1977 Atlatl Function: Comments on Howard's Views. Plains Anthropologist 22(76):159-160.