A double-action revolver works by allowing the shooter to both cock and fire the gun simply by pulling the trigger. A single-action revolver requires the shooter to cock the hammer with their thumb or free hand before pulling the trigger to fire a shot.
Double-action revolvers can be fired more quickly and with less effort than single-action revolvers. The double action also increases safety by allowing the gun to be carried un-cocked and reducing the risk of an accidental discharge. However, it can also result in a longer trigger pull and potentially reduced accuracy. Many double-action revolvers can also be used as single-action revolvers. This gives the shooter the option of cocking the gun before pulling the trigger for increased accuracy or simply pulling the trigger to cock the gun and fire for increased speed.
Some revolvers are referred to as double-action only or self-cocking. These revolvers lack the latch on the hammer to allow it to be cocked before the trigger is pulled and tend to have spurless or bobbed hammers that are often completely covered by the gun's frame. These guns are normally designed for concealed carry because the hammer of other revolvers could snag on clothing when drawn. The increased capability for concealing the revolver helps to offset the potentially reduced accuracy.