This awesome little coin was one the staples of the United States Monetary supply up until around 2000, at which time the coins were largely decommissioned.
These coins are now basically for the collector, and new coins only come in sets or purchases directly from the United States Mint.
Within the last 100 years the us has issued 4 different half dollars (minus commemoratives, the bicentennial, and other small variations)
This coin has a reeded edge with exactly 150 reeds or ridges. These ridges were implemented in an attempt to prevent handlers from shaving down the half dollars for there silver content. You may have noticed that all coins that have or do contain silver are reeded. The nickel and penny have never been reeded. (the Wartime Nickels are silver however, but that's exception)