The atlatl or spear-thrower is a tool that uses leverage to achieve greater velocity in dart-throwing, and includes a bearing surface which allows the user to temporarily store energy during the throw. It consists of a shaft with a cup or a spur, which may be integrated into the weapon or made separately and attached, in which the butt of the projectile, properly called a dart, rests. It is held near the end farthest from the cup, and the dart is thrown by the action of the upper arm and wrist. A 5 oz dart can be thrown at 100 mph and have as much impact as an arrow fired from a 60 lb compound bow. The dart is much more like an arrow. It has fletching added to stabilize flight and is quite flexible.
Both the atlatl and dart are springs that store energy. As the arm moves forward, both will flex and, if properly tuned, will spring back at the point of release, imparting the maximum amount of power. Weights (called banner stones) can be added to the atlatl to adjust the flex timing and properly shaped weights can actually help to silence the sound of the rushing atlatl. 

Because the atlatl is essentially a lever that doubles the length of the thrower's arm, it can easily deliver 200 times as much power and 6 times the range as a dart thrown like a traditional spear. Even with the increased mass of a normal spear, the atlatl-thrown dart clearly outpowers the spear.

Atlatl designs may include improvements such as thong loops to fit the fingers, the use of flexible shafts, and thinner, highly flexible darts for added power and range. Darts resemble large arrows or thin spears and are typically from  4 to 9 feet in length and 3/8” to 5/8” in diameter.
Another important improvement to the atlatl's design was the introduction of a small weight (between 60 and 80 grams) strapped to its mid-section. Some atlatlists maintain that stone weights add mass to the shaft of the device, causing resistance to acceleration when swung, which results in a more forceful and accurate launch of the dart. Other atlatlists claim that atlatl weights add only stability to a cast which results in greater accuracy.

Based on previous work done by William S. Webb, William R. Perkins claims that atlatl weights, commonly called "Bannerstones," are artifacts characterized by a centered hole in a symmetrically shaped carved or ground stone, shaped wide and flat with a drilled hole a little like a large wing nut, are a rather ingenious improvement to the design that created a silencing effect when swung, lowering the frequency of the telltale "zip" of an atlatl in use to a more subtle "woof" sound that did not travel as far and was less likely to alert prey or other humans. 

Wooden darts were known at least since the Middle Paleolithic (Schöningen, Torralba, Clacton-on-Sea and Kalambo Falls). While the atlatl is capable of casting a dart well over 100 meters, it is most accurately used at distances of 20 meters or less. An atlatl dart is capable of killing even the largest of animals at any distance that its thrower is capable of accurately reaching since more power is applied to longer shots than shorter shots. The accuracy of the atlatl and dart tends to decrease as the distance increases. The atlatl is believed to have been in use since the Upper Paleolithic (c. 30,000 BC)[4]. Most stratified European finds come from the Magdalenian (late upper Palaeolithic). In this period, elaborate pieces, often in the form of animals, are common. The earliest known example is a 27,000 year-old atlatl made of reindeer antler and found in France.

The atlatl has been used by early Native Americans as well. It seems to have been introduced during the immigration across the Bering Land Bridge, a wide section of exposed seabed that connected Asia and North America during the last Ice Age.

Every atlatl has 3 main parts - the handle (grip), the shaft, and the peg or socket. After that, everything is variable. Lengths range from 5 1/2" (Santa Barbara, Baja California) to 48" or more in Australia. Widths range from 1/4" to 8". Materials used include wood, bone, ivory, and antler. Some have pegs to hold the darts ("male") while others have sockets ("female"). They have been found with grooves, dart rests, finger holes, leather thongs, shell grips, antler handles, antler pegs, bone pegs, tooth pegs, carved grips, carved designs, paint, and bannerstones, which were only used in North America. 

Throwing a spear by hand involves the entire body. You step up, shift your weight, bring your arm forward, and flip your wrist to release the spear in one fluid motion. Throwing with an atlatl is exactly the same. So what makes the atlatl more effective? Physics. When you flip your wrist to throw the spear, your hand moves about 7" in 1/10 of a second. This 6 feet per second (about 4 mph) is added to the velocity of the spear. The final result is about 50 mph.

When you flip your wrist with a 24" atlatl, the peg end (and the attached dart) moves about 70" in that 1/10 of a second. This adds 60 feet per second (40 mph) to the velocity of the dart. The final result is about 90 mph. More speed means farther throws, harder hits, better penetration, and less time for the prey to react. That is what makes the atlatl so effective. And it is effective. In the past it has been used to hunt the "megabeasts". Atlatl points have been found in the bones of woolly mammoths and giant bison, and it is thought that man's use of this weapon is what led to the megabeasts' extinction.

How could one man kill a mammoth? He couldn't. But for ancient people, hunting was often a group activity. Small herds of animals were driven against a natural barrier (cliff, rock wall, river) and then everybody began to throw and stab. When the animals finally escaped, the wounded ones left behind were finished off.