An impact driver looks similar to a power drill at first, but there are a few key differences. First, an impact driver has a hex collet for installing different driver bits (and not drill bits), as opposed to the the chuck on a power drill. Second, an impact driver has a hammering action in the rotational direction for applying extra torque to help drive fasteners like screws into your workpiece. Impact drivers make tasks like screwing in long construction screws into dense woods a breeze. Keep in mind that if you are looking for a hammering direction along the axis of a tool (like a chiseling motion) you are looking for a hammer drill, not an impact driver.